When a group of children return to the surface after a day out trip to the caves that they won, every single person over 15 has disappeared. Meanwhile, Kat, her mum and her sister argue. She turns around and find out that they, too, are gone. The kids who'd been in the cave – Ami, Sadiq, Reese, Jordan and Callum – take a car to see what is going on but while going to the police station, Callum decides to leave. Sadiq calls for him and Callum almost hits Sadiq with a brick on purpose. They leave the car and enter a supermarket at Ami's request. Kat finds her next door neighbor, Liam, trapped in his room because his mother grounded him for 5 minutes. As his mother disappeared with the rest of the adults, she was unable to let him out. Kat gets him out and they find an ice cream van. After she gives Liam an ice cream, they head to the supermarket. Just before Sadiq puts his hand in the till, Kat appears and confronts him. The group (Sadiq, Jordan, Ami and Reese) then go to get Sadiq's stepsister, Frankie, and his neighbor, Tia, at his house and Jordan's brother, Jeffrey, who has cerebral palsy, at his school. The group then head to a hotel and lock out all of the other kids who are trying to get in, including Kat and Liam.

Callum's new gang intend to take over the City Hotel, using Kat to gain access. Meanwhile, Reese visits the library to learn more about the Sparticle Project, and sees 'ghosts' of the adults there. Later the two find out the adults are still there but in another dimension. The group meets a girl named Holly, who was staying in the hotel when the adults disappeared.

While visiting the university to find food, Reese discovers a message from Professor Dora Petty, better known as Doomsday Dora, explaining how the adults disappeared and urging the children to help them return. Meanwhile, Holly is held hostage by the only remaining adult, Anita, who received a heart transplant, and as a result of having received the heart of a fourteen year old was not sent to the parallel dimension with the other adults.

Note: Guest Appearance of Doomsday Dora and Anita.

Doomsday Dora's message has warned the children they must reunite the two parallel worlds quickly or adults and children will remain separated permanently. The children decide to choose who goes on the road to the Sparticle Project and who stays behind to look after Liam and Frankie by an 'Apprentice'-style challenge to source power for the City Hotel. They eventually appoint Kat and Sadiq as joint leaders of the ‘Questers’, who search for the Sparticle Project (Kat, Sadiq, Holly, Jordan, Ami and Reese) and Jeffrey and Tia as leaders of the ‘Ranchers’ (Jeffrey, Tia, Liam and Frankie), who remain at the hotel.

The Questers discover a fairground, where Jordan, Holly and Ami take being kids way too far, and nearly kill themselves on a runaway waltzer, until Muna (a child caught between the parallel worlds) comes to the rescue. The lack of grid power has led to the failure of the national water supply. Fresh water becomes the latest challenge for the Ranchers, and Frankie goes native in her attempts to find and save the precious resource.

Note: Guest Appearance of Muna and Doomsday Dora

A postcode given to Reese via Psychic Sarah at the fairground leads the Questers to a simulator where scientists were trained how to run the Sparticle Project. Ami, Jordan and Holly get trapped in the room with the prototype collider's super-cooling systems running and the temperature plummeting towards absolute zero. At the City Hotel, a fox has been at the chickens and the children decide to trap it. This is very tricky, but when they finally track down the animal and are set to destroy it, they decide on a better course of action.

While the team are on their way to the Sparticle Project, Ami is captured in the woods by the Water Rats – a group who love life messing around on the river. The Water Rats are at war with the Menaces – and the Questers, persuaded by Ami, decide to help. Will Ami swap the seriousness of the Quest for a kid's life of fun and games? Meanwhile, Jeffrey is keen to help out more, but his wheelchair needs more power. Tia and Jeffrey discover a satellite communication system which allows them to send a message into the ether, asking anyone out there for the batteries Jeffrey needs. They arrive back at the hotel to a package − it is from Anita at the university and it comes with a message.

The Questers are intrigued by Head Boy Jeremy and his posh boarding school. However, they are soon locked out and Jordan is forced to leave the tribe to become a true public school believer. Camped outside the school, ex-pupils Ernesto and his rebel gang recruit the Sparticles to overthrow Jeremy's regime and rescue the Unsuitables – the 'less-than-perfects' who do the dirty work for Jeremy and his cadets. The Ranchers at the City Hotel work out how to bypass the first door at the Sparticle Project. Working with Anita at the university, they come up with an ingenious solution, but now they need to get the key to the Questers out on the road. Callum, who is keen to impress Kat, offers to collect the key and bring it to the Questers.

The Questers on their way to the Sparticle Project discover a bucolic village run on communal principals. Reese 'sees' Muna again and with the help of Tamsin, one of the village kids, Kat figures out that the wormhole events are occurring at points where laylines intersect. Some of the Questers, however, have been caught red-handed stealing food and are made to stand trial in the children's court where the issue is whether stealing to survive is justified. Jeffrey is proud of his abundant garden, but when a few hungry girls turn up at the hotel, he finds himself at war.

Note: Guest Appearance of Muna

The Ranchers have invited a tribe of seriously idle girls into their hotel. As they take advantage of the hotel and the Ranchers, the Ranchers are forced to fight back − but who will be turfed out of their home? Holly is anxious when she realizes the journey to the Sparticle Project is coming to its conclusion. She leaves her fellow Questers trapped in an underground nuclear bunker, but there is another force at work. A computer which thinks there has been a nuclear war competes against the ingenuity of the children in a battle of wits.

The Questers discover an alarming new threat. Without the adults, and the automatic cooling systems, the world's nuclear power plants are melting down and threaten to destroy the earth. The Questers have to get a message to the adults – but how? Callum arrives to collect the key to the Sparticle Project from the Ranchers, only to discover them homeless. Tia and Jeffrey don't trust Callum after past encounters. Unfortunately, the key has been lost and sold, and Callum is the only hope to getting it back and to reuniting them with their friends.

The Questers and Ranchers are reunited at Black Tor Mine where the adults were separated from the children by the machine of the Sparticle Project. But another tribe – the Mystic Moles, who are the children of the scientists working there – won't let anyone through the doors. Callum arrives with the dictaphone, the key to opening the Sparticle Project. The Sparticles face a series of challenges before they get to their greatest obstacle. Although they are successful reuniting the worlds, the two worlds are still unstable. Elsewhere, Reese and Holly came across a electricity leak. Reese and Muna use their powers to hold the electricity in place. But the reunification process takes too long and destroys Muna. Reese tries to hold the electricity in place on her own, despite Holly's protests. In the control room, Kat, Sadiq and the adults watch the event while Liam, Frankie, Ami, Jordan, Jeffrey and Dora attempt to hold the Luminite, a mineral that magnifies energy, in place to fix the damage caused to the Sparticle Project by the misinformed Mystic Meg, leader of the Mystic Moles. Kat tries to convince her dad to shut down the Sparticle Project and save Reese. The other adults attempt to stop him, but he shuts down the project, saving Reese. This disrupts the realignment process and the two worlds split again. Doomsday Dora tells the Questers to travel to the Quantum Nexus (hinting a second series). Just before Kat's dad disappears, he gives her a code to shut down the world's nuclear power plants. Sadiq comforts her about the failed realignment. The Sparticles regroup and Liam suggests the group should journey to the Quantum Nexus and attempt to bring the adults back again.

Note: Final Appearance of Kat, Jordan and Ami.

After a year of searching for the Quantum Nexus, most of the tribe has split up. Jordan and Ami have gone to France, Kat is sorting out the nuclear power plants but everyone else reunites when they realize the key from Doomsday Dora fits into a stone head. Unfortunately, the head is in a stadium owned by Fizzy and there is also the matter that there is a traitor within their tribe. Reese is captured and the dims threaten to feed her to the lion if the Sparticles lose the competition between Fizzy’s Dim Army and The Sparticles to win the key to the Quantum Nexus. The lion is revealed to be a hoax and Holly is revealed to be the traitor, accepting a bag of Fizzys for doing a job for Fizzy. She vows to find the Quantum Nexus first and destroy it to ensure the adults never return. She and Serena take off and the Sparticles take the Stone Head back to the Spartivan and set off on a race to the Quantum Nexus.

The Sparticles and Holly and Serena arrive at the museum that the stone head belongs to and plan to decode the message on the Stone Head, but the Sparticles get caught up in a plan with another tribe, the Featherheads, to raid the museum in order to get gold to melt down to turn into Fizzys to use to buy fuel. Holly and Serena break into the museum and use an ogham has decoder to translate the message on the Stone Head, which was written on a piece of paper that they stole from Reese. While Jeffery and a member of the Featherheads work on a machine turning waste into fuel, the remaining Featherheads rob the gold from the museum, including the Decoder. Reese attempts to get it back but is caught in the diggers bucket and is nearly killed. The Sparticles chase the digger down the road but it gets stuck and Reese drops the Decoder. The digger destroys the Decoder and Rocky drops the bucket and lets Reese out. Before they leave, Reese reveals that before it was destroyed, she saw the message decoded. They leave, and Rocky's brother finds a note stating that he has stowed away with the Sparticles to get their mum back.

Note: first appearance of Rocky.

The Sparticles and Holly and Serena bump into a circus tribe while searching for the white horse. For Serena, will it be a happy reunion with her sister?

The Sparticles, Holly and Serena all go to Peace City on their way to the River Artos. As Reese is being pulled through as she tells Sadiq, "Peace City might be the Quantum Nexus." Holly and Serena lose the sword (which is taken by Rocky in disguise). Fizzy puts up wanted posters for the Sparticles. Reese meets another person who has special powers named Huen. Tensions rise as Ernesto and Callum arrive. As Holly and Serena exit, Holly spots the sword and shows Serena it hadn't dissolved in the acid bath. She grabs it and they decide to head off for Water Mint Mill.

The Sparticles travel to an abandoned mill where a supposed creature has been eating children. There, Tia and Jeffrey's relationship comes under strain and Rocky shows his true colors as he snatches the necklace Tia gave to Jeffrey and throws it in the River blaming Jeffery for the incident. The Sparticles get their next clue, which leads them closer to the Quantum Nexus.

The Sparticles find the stone which opens the Quantum Nexus but Jeffrey gets poisoned by itcyflax flower so therefore the Sparticles go to a castle to get a treatment but Holly messed up their car so Holly and Serena have to give them a ride to a castle that has the cure but the Sparticles and Holly and Serena soon get caught up in duels when they lose their sword.

Note: final appearance of Huen.

A tribe of Traders lock up the Sparticles and accuse them of stealing their shipment which was to be given to Fizzy. They soon discover that the shipment was chocolate and that Fizzy is going to make an army using these. Serena and Holly are then captured and put into a room as the Traders thought they were Sparticles. After an escape planned by Frankie, Liam and Reese, they tried to rescue the others but were unfortunately captured again but Frankie and Liam escaped and found the balaclava and shipment and they discover that it's Skinny as he was 'sick' of taking orders from his boss. He is then arrested by Callum for breaking one of the rules but soon freed to help the Sparticles. Rocky stayed behind to help the Sparticles rather than Callum. Fizzy turns up and the chocolate is melted and Rocky tells to stay off the Quantum Nexus and the Sparticles to get chocolate and biscuits and it was agreed except of Fizzy who was frustrated. The Sparticles get the treasures back and are going to try to find the Stone of Artos.

The Treasure Hunt is coming together with the discovery of another vital clue in the race to the Quantum Nexus, but the return of Ernesto leads to questions – exactly whose side is the Rebel on? Later on, Reese sees Muna and it is revealed that Muna came back in limbo at the Sparticle Mystery. Muna also tells Reese that it is dangerous to realign the 2 worlds as there are many more dimensions that could destroy them. Later on, it is discovered that Sadiq tells the other Sparticles that Serena is a double agent.

Note: first main appearance of Ernesto and guest appearance of Muna.

The Sparticles reach the Quantum Nexus at last and the race is on to see if they can bring back the adults or stay in the world of Emperor Fizzy forever. A curious old friend looks set to help. Dora had set up a hologram version of herself called 'HoloDora', whom she believes to be Dora's daughter and when the children are detected by 'HoloDora', she change to help them to bring back the dimension with the parents. Reese attempts to modify the magnetics of the Quantum Nexus in order to damage the machine due to her worries of connect the wrong dimensions. Reese fails to do this, as she does not know the two dimensions are connected. The wrong dimension is set to come to Earth, which results in the adults – now teenagers – arriving.

Note: final appearance of Callum, Tia, Jeffery and Liam.

After bringing the teenage versions of their parents to their dimension, the remaining Sparticles are locked up by the monstrous Queen Kylie. During a rescue mission, Reese teams up another sensitive named Aris, and they manage to send one of the teen parents home and escape with Holly's teen mother Kim. While heading to the resistance HQ, Reese created a plan to send Kylie home so the Sparticles head back to the Citadel to rescue Aris.

Dora's Neuroscrambler machine goes wrong, causing Aris to lose his memory. Meanwhile, a resistance member Jenna snitches on the Sparticles via a Truthline and joins the bounty hunters Fizzy and Bryan. They kidnap Frankie while she's away from the others but Ernesto leads them to an abandoned factory, where the Sparticles manage to rescue Frankie and slow down the bounty hunters but also manage to get Ernesto fired from the resistance. Meanwhile, Dora helps Aris escape after wiping his memory and Kim discovers she is Holly's teen Mother.

The Sparticles, on the run from the Bounty Hunters, stop in at a trading post only to find a layline and another sensitive named Orion like the constellation. Sadiq, Holly, Frankie and Kim are locked up while looking for the boy, Orion, but are soon rescued by Reese and Aris before the Bounty Hunters find them. Orion shows Reese and Aris a book which relates to their dreams and the laylines. After Serena gets Ernesto accidentally tied up and turned into a trap, the rest of the Sparticles are trapped but are rescued by Orion who sends Jenna home, taking Fizzy and Bryan's relationship down a notch. The Sparticles escape but leave Orion and his friend behind to be mind-wiped.

Note: First Appearance of Orion and last appearance of Jenna.

Reese uses her 'powers' and the help of Holodora to work out the secret to ridding the world of Queen Kylie and the Teen Parents. Reese finds out that the 'Red Dragon' comet is going to pass by in September and that it's made of luminite. Meanwhile, Ernesto and Serena are attempting to earn Rat's trust again by going through rather straining military exercises, Fizzy and Bryan make a breakthrough with finding the Sparticles and Dora finds out how to get Orion to connect with Reese.

Note: First regular appearance of HoloDora (voice only.)

Ernesto and Serena join forces with the resistance to infiltrate the Citadel and attempt to rescue Orion, but are actually on a rescue mission for the toys Kylie locked away. At the resistance HQ, the two meet Rat's child – which will eventually grow up to be Ernesto! Meanwhile, Kylie is impatient to learn the Sparticles plan, she has Dora trick Orian to connect to Reese and she accidentally tipping them off about the Resistance's plan and their own.

Note: Final Appearance of Rat.

When Frankie's rabbit goes missing, the Sparticles find themselves locked up by a 'friend' of Kylie's named Lady Lucy-this"friend" has never actually visited or met Queen Kylie in real life. Frankie escapes and befriends her servant Robyn, who reveals that she is the real Lady Lucy and the imposter stole her identity. Serena and Ernesto arrive at the forest in time to rescue everyone and discover the real Lady Lucy is a sensitive. Meanwhile at the Citadel, Kylie wipes Orion's mind and discovers the Sparticle's plan. Orion explains the plan about the "special places" Reese spoke about to be several points called laylines across the country mirroring the Orion constellation where the sensitives are going to stand.

Note: Fizzy, Bryan and HoloDora are absent in this episode

The Sparticles head to a 'Quantum Anomaly' known as 'The Zone' to visit a sensitive with healing powers so he can make Holly recover from a mysterious illness. The sensitive, known as Jason, reveals that Holly is pregnant and in perfect health, much to Ernesto's shock and delight. Meanwhile the bounty hunters chase Reese and Aris into a Quantum Fracture where the two find themselves in the adult dimension, and manage to download HoloDora onto a tablet and return home to continue on with the mission.

Note: Queen Kylie, Orion, Dora and Erimon are absent in this episode.

Queen Boudicca's daughter wants to help the Sparticles fight against Queen Kylie but she urgently needs to return to her own dimension to fight the Romans. Serena, Reese and HoloDora send Bua home, to Sadiq's dismay, of losing their fifth sensitive, and to Aris' annoyance that Reese did not allow him to help send Bua home. Serena and Ernesto take Fizzy and Bryan's jeep (which the Fisher tribe stole the keys for) and part ways which they go to the citadel to rescue Orion, while Sadiq and the others search for the sixth sensitive.

Note: Erimon is absent in this episode.

Note: Guest Appearance of Bua.

After watching Kylie play with Orion's mind, Erimon decides that he hates his sister and regrets helping her become Queen. Meanwhile Serena and Ernesto break Orion out of the citadel, helping him remember who the true Sparticles are with Reese's friendship bracelet. HoloDora also enters the Citadel and finds Dora, only to be shocked when she finds out that her teen mother is helping the evil Queen, and then accidentally mentioning the Red Dragon comet. Kylie uses this information and takes matters into her own hands by heading to the Circle of Perpetual Time with the after overhearing Dora and Erimon plotting against her. Serena, Ernesto and Orion successfully escape the Citadel, but with the knowledge that Kylie knows the full Sparticle plan.

The Sparticles arrive at a 'haunted' house and find the next Sensitive, who doesn't know how to use his powers. However, when Aris disappears, the rest of the Sparticles vanish one by one. The source of the kidnappings is Queen Kylie, who reached the house first and is aware of a different sensitive who turns out to be the 'ghost' in the house. Reese and Yanx have the perfect opportunity to send Kylie home but are stopped by Aris, who believes he is saving his mother and leaves with her. The Sparticles leave the mansion with confirmation that Orion has been broken out of the citadel and that Kylie is planning to block the Sensonet at the Circle of Perpetual Time.

Note: Serena, Ernesto, Orion, Dora, Erimon, Fizzy, Bryan and HoloDora are absent in this episode.

Kylie and The Sparticles are held up in their missions by a bridge guarded by apparently cannibal trolls. Sadiq and Serena break up in an argument and Kylie tests the Neuroscrambler on Sadiq when she works with the Troll Queen Trina and ties him up and wipes his memories of the day. Aris rejoins the Sparticles as a spy for Kylie.

The Sparticles arrive at a lighthouse and stay there while Holly gives birth, only to find the oldest man in the world still living there. Ernesto follows him to his garden, and discovers the Circle of Perpetual Time! Frankie, Reese and later Sadiq discover that Aris is a spy for Kylie, who is at the lighthouse setting up the Neuroscrambler. Dora and Erimon arrive with the transmitter, and Aris discovers Kylie has been lying to him and rejoins the Sparticles who believe The Keeper is the final sensitive. Kim reveals to Holly that she is her Teen Mum, but then issues arrive when The Keeper isn't the final sensitive.

The comet approaches, and the Sparticles discover that Holly's newborn baby is the final sensitive. The Neuroscrambler breaks down, due to HoloDora's interference, Kylie orders Dora to repair it, and threatens to push Erimon off the cliff if she doesn't. Dora attempts to fix it but HoloDora messes with the Neuroscrambler's coding, leaving it stuck on mind-wipe mode, meaning the only way to save the sensitives is to turn it off. Dora still turns it on due to her feelings for Erimon. Aris explains Kylie's plan to burn out the minds of the Sensitives using the comet including the baby. Bryan thinks that the baby won't be affected to greatly as she doesn't know much, which infuriates Fizzy, who states that's why Bryan never made a good father in his future. Fizzy helps the Sparticles break into the lighthouse and disable the Neuroscrambler while Aris stays with the keeper, discovering that he dreams about the comet too. Kylie shuts Fizzy and the Sparticles outside, believing she is unable to trust anyone after Erimon's 'betrayal'. HoloDora shows Kylie, Erimon and Dora and image of Holly and Ernesto's daughter, and explain that if she goes ahead with her plan, she will fry her mind. Kylie remains ignorant, even with Ernesto's plead to spare her and the sensitives. Kim brings the baby to Reese and Aris, but the sensitives can't connect with her. Kylie attempts one final try at convincing Aris not to line up, but instead he heals her scar with Jason's powers. Aris figures out the keeper's riddles and learns that the herb garden isn't the circle of perpetual time, but the old man was. They quickly race to the lighthouse where the old man is. The Keeper's powers activate when he holds Holly's baby and the sensitive link up. The comet passes over, but nothing happens, because HoloDora steals the power and becomes real. Upon realizing what she really looked like, Dora convinces her to do the right thing and send the teen parents home. She releases the energy into a portal, which sends, Kylie, Erimon, Dora, Bryan, Kim, Orion and all the other teen parents back to their times. Holly is searching for the others when her mother emerges, and they embrace. Fizzy's dad and other adults appear as well. HoloDora had altered the quantum energy transfer to bring back their proper parents (possibly losing the old man in the process, who appeared as a hologram with HoloDora). Holly and Ernesto present Kim with her granddaughter (whom they named 'Kimmy', after her.). The Sparticles rejoice and celebrate the victory in bringing back their parents, bringing their quest to an end. The episode and show ends on a celebratory "We did it!"

Note: Final appearance of Sadiq, Reese, Aris, Frankie, Holly, Ernesto, Serena, Kim, Kylie, Dora, Erimon, Fizzy, Bryan and HoloDora.

Note: This is the final episode.