One of the pupils in Stephen's class, called Robert, paints a accurate picture of another planet, Rexel 4. Stephen jaunts back to the Lab and tells John and Tim about the picture. He also tells them that he thinks his teacher, Elizabeth, is breaking-out. The next day at school Stephen is in the middle of jaunting home when Elizabeth walks in and sees him. She thinks that the telepathy she can hear between Stephen, John and Tim is just Stephen throwing his voice to trick her. The next day Stephen notices that Robert's picture has changed colour from a bright sunny picture to a dark stormy picture. John finds another picture of another planet, QX5, painted by another student, it also appeared to change colour. Tim found a newspaper report that the was a serious disturbance at the school where the QX5 picture was painted, and another report that a similar picture had been exorcised because when is showed a storm the local school children were uncontrollable. The next day Stephen noticed a similar trend at his school. Stephen asks John to meet Elizabeth in an attempt to talk to her. Stephen takes John to meet Elizabeth at school, but she refuses to believe John. Elizabeth leaves the room, but John jaunts in front of her to stop her, this starts her breaking-out. She tries to run away again, but Stephen jaunts right in front of her. She panics and jaunts away, out of control.

John and Stephen jaunt into Hyperspace to look for Elizabeth. When they find her she jaunts back to the classroom. John and Stephen join her and take her to the Lab. The next day at school is very disrupted. John, Stephen and Elizabeth return to the school to look at the picture. John wants to take the picture back to the Lab, but Elizabeth says it might be dangerous. The next day Robert hands out blue and green badges, Elizabeth takes a blue, Stephen a green. Chris arrives at the Lab after a fight with his brother. He tells John the fight was because Chris is a green and Ginge was a blue. When John took Chris's badge off he returned to normal. At school a fight started in the classroom, even Stephen and Elizabeth started fighting. John and Stephen returned to the school that night and set up a video camera to try to record the picture changing. Elizabeth was walking home when she passed a junk shop and noticed another strange picture in the window. The picture at the school and the picture in the shop changed, a group of boys surrounded Elizabeth.

Elizabeth called for help. John and Stephen jaunted to help her, the boys ran way. Stephen returned to the school and found the video camera smashed. John went to the junk shop and bought the painting. John found out that Robert lives above the shop. Stephen was invited to Robert's home that afternoon. Robert took Stephen to the cellar. The cellar was full of strange pictures and boxes of blue and green badges. Robert told Stephen that he did not know his parents, and that his grandfather was not really his grandfather. Robert gave Stephen a picture that he took to the Lab. John and Tim were examining the picture that John bought. Tim gave it a Neutron examination, the picture destroyed itself. Tim found that Robert does not appear in official records. Robert used the picture he gave to Stephen to spy on the Tomorrow People in the Lab. John returned to the shop and tried to go into the cellar. Robert's grandfather stopped him. John returned to the Lab. Robert took control of John making him use his telekinesis to damage the Lab. John then disappeared.

John had been kidnapped by Robert and locked in a room in the cellar, something had removed by telepathic abilities. Stephen jaunted to the shop to search for John. He found him in the cellar, but could not release him. Robert came down into the cellar, Stephen's stun gun had no effect, so he ran out. Chris took two friends and broke into the shop and the cellar. The two friends started misbehaving, alerting Robert's grandfather, the friends ran away. Chris could not open the door to release John, so he left as well. The next day Elizabeth tried to remove the picture, but Robert stopped her and left some of the school boys to guard it. He then left. Chris intercepted Robert, but he ran away, leaving some books behind. Robert told a policeman that Chris was following him. Chris took the books back to the Lab. One of the books was volume 4 of the Decline and Fall of the Roman Empire. Tim realised that there was a link to the fall of the Roman Empire, they also broke into two factions, blue and green. Robert told his grandfather that he was leaving , and to tell the police that he was missing. He then took John. Chris went to help Elizabeth at the school, but was spotted by the police, eventually they caught him when he crashed. They charged him with Robert's disappearance. The police took Chris to the shop to look for Robert. They went to the cellar. The cellar was empty, all of the pictures had gone, as had John.

Chris managed to escape and locked the police and Robert's grandfather in the cellar. Robert had taken John to find more information about him. He told John that he was an alien, born on Earth, his human form was an egg. When hatching his species require a lot of human aggressive energy to complete the transformation. His mother was also born and hatched on Earth. The energy she required caused the destruction of the Roman Empire, this time there are many thousand hatching. John persuaded Robert to release him, so that the Tomorrow People could try to find a way to save the humans and allow the aliens to hatch. John asked Tim if there were galactic records on the aliens (called Denagelee), Tim had none. Robert and the other Denagelee started to hatch. Stephen had an idea that if they could put everyone to sleep their REM sleep could provide the energy without hurting other people. Stephen suggested that they could build a giant stun gun in space to stun everyone on Earth. John, Stephen and Elizabeth collected the parts needed and took them to the watchdog satellite to build the stun gun. The stun gun worked, stunning everyone, but allowed them to dream the violence the Denagelee required. The Denagelee left the Earth, and agreed not to come back to the Earth. John, Stephen and Elizabeth returned to Earth. Stephen erased the memories of the policemen trying to catch Chris. When the policemen woke up they let Chris go free.

John and Stephen have the same strange dream of Peter running through a forest. In a second dream he shows them a vase. After looking through several thousand pictures of vases they find the vase. Stephen contacts Professor Cawston and pretends that he demonstrates telepathic abilities only when he holds a picture of the vase, Professor Garner who looks after the vase is fooled into bringing the vase to Stephen. When Stephen gets the lid of the vase he jaunts back to the Lab. The lid has strange markings which are a Neutron Interton Diagram, they decided to build the device. Peter is in a gladiator training school in ancient Roman Britain. The finished device is a small disk, nothing happens when Chris and Elizabeth pick it up. When Stephen picks it up he disappears.

Stephen has been caught in a Time Trap. John wants to build another device to try to find Stephen. When Stephen tells the Guardian of Time about Peter, he is released. The Guardian is called Zenon and is Peter's Grandfather. He warns Stephen not to build another Time Disk as its user could be lost in eternity. He gives him five Time Disks to take back so that the Tomorrow People can try to help Peter. Stephen gets back to the Lab just in time to stop John using another Time Disk that he has made. They find out from Professor Garner that the vase comes from a gladiator school in Silchester run by Gaius. John, Stephen, Elizabeth and Chris return to ancient Roman Britain. They go to the gladiator school and try to sell Stephen and Chris, but they only buy Stephen. They then find that their telepathic abilities have disappeared. Stephen finds Peter when he is locked in the dungeon. Peter thinks that someone is transmitting a radiation that is inhibiting their telepathic abilities. Gaius selects Stephen to be tested by fighting. They try to buy Stephen back, but Gaius refuses. Elizabeth thinks Gaius knows they are telepaths. Stephen is defeated.

Gaius spared Stephen, and sent him down to the dungeon. Another trainee, Cotus, is also in the same cell, he is due to be sent to the horse trials to be killed. John, Elizabeth and Chris break into the gladiator school that night. They all hear a steam engine, 16 centuries before it was invented. Peter suspects that Gaius is responsible for the Time Warp. Chris manages to free Stephen, Peter and Cotus. Peter tries to arrest Gaius, but he escapes in a Time Pump. They release all the trainee gladiators before the Time Pump explodes. They then return to the 20th Century, but the Lab is not there. Cotus returns to the gladiator school and starts to repair the steam engine. John thinks that the Earth has been invaded from outer space.

They discover that the Roman Empire has not died out in the 3rd or 4th century, but developed much technology earlier. They return to ancient Britain. Gaius is in the Roman 20th century and over hears the Tomorrow People's conversation. Gaius also returns to ancient Britain. The Tomorrow People go to the gladiator school and destroy the remains of the steam engine. Cotus also returns to the gladiator school just before Gaius returns. They are all captured. Cotus tries to stop the Tomorrow People being killed, and is knocked-out by one of Gaius's guards. All the Gaius and his guards all disappeared as Cotus lost his memory.

Stephen goes under cover to investigate an organisation called The Doomsday Men. The grandson of the leader goes to a school called Glen College. Stephen finds out that the school is a training ground for the Doomsday Men, and that General McLelland is planning a suicide mission. Douglas asks Stephen to join the organisation, he also finds out the the mission is called Operation Silver Thread and they will try to stop the signing of a peace treaty. Stephen was summoned to the gym where he had to fight several other boys with a sabre.

Stephen managed to disarm the boys, as he used to be a schoolboy fencing champion. He was told the Operation Silver Thread was to happen the next day, and it was to involve the Damoclese space station. One of the crew on the Damoclese had an accident while working outside the space station, and was blasted away from the space station. John, Stephen and Elizabeth used a matter transporter to take Chris's van into space to rescue the crew man. They took him back to the Lab, and explained the situation to him. Stephen returned to the school. That night Stephen was initiated in to The Doomsday Men. On the Damoclese General McLelland captured the space station by pretending to be the relief crew.

John, Stephen and Elizabeth decided to try to re-capture the Damoclese. Lee Wan told them that there was a dead man's switch that would launch the nuclear missiles. John decided to take Lee Wan's space suit, floated past the Damoclese and found that the dead man's switch was in use. The Doomsday Men transmitted their demands to the United Nations who postponed the signing of the peace treaty. The boys at the school went on a cross-country run. Tim matched the voice from the Damoclese with General McLelland. On the cross-country run Stephen saw Douglas being kidnapped, but was knocked unconscious.

Some of the other boys find Stephen and take him back to the school. Douglas went willingly with the kidnappers to an old deserted windmill. Dr. Laird took some spare clothes to Douglas, Stephen and Paul, one of the school boys, hid in the back of his car, but were captured. Dr. Laird was going to shoot them, but Stephen activated the matter transporter belts taking Paul and Douglas back to the Lab. Tim re-educated Paul and Douglas, showing them how bad war is. They decided to help. John put on Lee Wan's space suit and drifted up to the space station, General McLelland was at the dead man's handle, so that plan was put into action. Douglas matter transported to the station, followed by Stephen and Lee Wan. Unfortunately one of the other Doomsday Men interrupted and the General let go of they tried to stop the missiles firing, but could not find the key. John and Elizabeth tried to move the station so the missiles would miss the Earth, but could not dead man's handle. Stephen, Douglas and Lee Wan tried to find a way to move the station. Douglas threw his bagpipes into the machinery that made the living quarters spin. This made the whole station spin, when the missiles fired they went into the sun.