John and Stephen find themselves with two mysteries to investigate - the possibility that Stephen's new teacher Elizabeth M'Bondo is a Tomorrow Person and some worryingly accurate paintings of alien planets.

John and Stephen follow Liz into hyperspace, where they manage to rescue her and return her to the lab. Convinced of their story, she agrees to help them investigate the paintings, which seem to induce violence in those around them.

John and Stephen rescue Liz from the youths and find out about the second painting. John buys it from a man who turns out to be Robert's grandfather and takes it back to the lab, only to find out it may be a trap.

John is being held prisoner by Robert in the cellar of the antique shop, unable to use his powers. Chris attempts to rescue him but only succeeds in getting himself in trouble with the police.

Robert explains to John that his race uses violent energy as a power source. If they stay on Earth, they will die, but the violence needed to power their departure will completely destroy Earth's civilisation.

John and Stephen both begin having dreams about Peter and realise he is asking for help, but first they must track down a Roman vase that also appears in the dream.

Stephen is transported to the Hall of the Time Guardians where he meets Zenon, Peter's grandfather. Peter has become lost in the past and his only hope of rescue lies with the Tomorrow People.

John, Liz and Chris plan an attack on the gladiator training school to try and rescue Stephen and Peter, but none of them have realised Gaius' true nature.

History has been altered and the Roman Empire now encompasses half the galaxy. The Tomorrow People and their friends must return to the past to put things right, but Gaius is in hot pursuit.

A new peace treaty is about to be signed but the Tomorrow People are worried about the Doomsday Men, an organisation dedicated to the perpetuation of war. Stephen is sent undercover at the same school, as the grandson of the group's leader.

Stephen earns the respect of Douglas and the others and is invited to join the Doomsday Men. Meanwhile, an accident at the Damocles space station leaves an astronaut in danger, so the Tomorrow People decide to intervene.

The Damocles is in the hands of the Doomsday Men and the Tomorrow People are powerless to act. Any attempt at intervention and McLelland will throw the dead man's switch and launch nuclear missiles towards the Earth.