A Russian girl escapes from two men in a car in London. The Lab comes under attack, radiation prevents John, Elizabeth and Mike from escaping, people in masks break in. The girl is a telepath working for the KGB. Elizabeth is brought round by Major Turner of the SIS, who wants to know where the Russian girl Pavla Vlasiva is hiding. Major Turner read Elizabeth's mind and found that see did not know about Pavla. Major Turner revived John and Mike. Major Turner told them that Pavla had been reading the minds of the delegates at the NATO conference. The SIS wanted to capture Pavla so that they could erase her memory, or kill her if necessary. John, Elizabeth and Mike started looking for Pavla. Mike found Pavla at a disco. She saw some KGB agents and made an excuse and left. The KGB agents questioned Mike. They followed him out the back of the disco, they threatened to kill him unless Pavla came out of hiding. She came out of her hiding place Mike told her to run and then jaunted. Mike lost her again. Pavla went to a radio station to try to contact her parents. The radio producer tipped of the KGB. When they arrived Pavla saw the agent she contacted Mike telepathically, he jaunted to the radio studio. The KGB agent knocked him out.

The KGB agent took Pavla and Mike. John and Elizabeth jaunted to the studio. Major Turner was already there, she told them what had happened. Mike regained consciousness, before they could put him back to sleep, he jaunted back to the Lab. John and Elizabeth helped Mike to contact Pavla, she was still at the Russian Embassy. John and Mike jaunted to try to rescue her, she refused to go. They returned to the Lab without her. Major Turner followed a KGB car that left the Embassy with Pavla in it. The KGB man realised that they were being followed, after a car chase the KGB car crashed. Pavla was taken away in an ambulance, Major Turner had commandeered it and took it to her to an SIS building. John found the building. John, Elizabeth and Mike jaunted to Pavla's room. Major Turner was using a machine to extract all the information from her mind. John and Elizabeth went to try to get help to try to stop Pavla being harmed. Mike jaunted to the Russian Embassy. Mike told the KGB General that the SIS had Pavla. John and Elizabeth managed to stop the brain drain. Mike jaunted to Pavla's room and told them what he had done. Major Turner and Pavla told them that they must get out of the room and leave Pavla alone. Major Turner told them that every important KGB agent has a small explosive device surgically implanted that can be remotely detonated. Mike went back in the room to try to help her, but the explosive was triggered. Pavla jumped through the window and exploded.

John, Elizabeth and Tim decided that Mike needs a holiday to help him get over Pavla. John and Elizabeth took him to the planet Gallia. John wanted to investigate the end of the civilisation 2000 years earlier. In a mine young boys are force to work by aliens. John and Elizabeth think Timus may have had an ulterior motive for suggesting they visit Gallia. Two of the boys escape from the mine, the leader of the aliens ordered his guards to recapture them. The Tomorrow People heard the hunting horn of the guards, and then spotted the boys and the guards. John and Mike rescued the boys and took them back to their base. They were unable to understand their language. They eventually found out that their names are Trig and Trog. John and Mike took Trog to some of the settlements. When Mike and Trog went into a village, all the people ran away. Two of the aliens rode up and captured them.

Mike and Trog were taken to the mine, they took Trog's matter transporter belt. John scouted around and found a Klepton spaceship. Mike managed to grab one of the Klepton's guns and forced them to release Trog and return the matter transporter belt. Mike and Trog returned to the base. Timus paid an unofficial visit to the base. He told them that the Galactic Federation was not taking action to stop the Kleptons, but just discussing it. He also said that the Kleptons use the boys as hostages, as well as workers. He suggested that the slaves should be set free, and the Kleptons forced to leave the planet. The Tomorrow People formulated a plan to attack at night, when most of the Kleptons are asleep in the spaceship. John and Mike stunned the guards and made their way into the mine, followed by Elizabeth, Trig and Trog. Gremlon found the stunned guards at the entrance of the mine and blocked the escape route. After a chase Mike managed to overpower Gremlon. The Tomorrow People transported the spaceship to a barren planet Stixus, and removed the ship engines, stranding the Klepton crew.

Mike's band, the Fresh Hearts, is playing. A man, Jake, asks Elizabeth if he could become the band's manager. The band becomes very excited by Jake's offer. Jake holds a strange ritual. Elizabeth tells John that she thinks that Jake is a cheat and a fraud. At a rehearsal Jake asks Mike to play his drums to the special rhythm on a metronome, the cleaner working in the room starts to act very strangely and is taken outside to recover. Jake says it is their music that affected her. Jake arranged for Mike Harding to watch them that evening. Mike Harding was impressed, and arranged for them to play live on television. Elizabeth finds out that Jake is actually Professor James Marsden, the leader of a religious sect The Hearts of Sogguth. She persuades John of infiltrate the group. John is initiated into The Hearts of Sogguth. John thinks they are harmless. Jake gave Mike the Heart of Sogguth drum to play, but warned him not to play the special rhythm. Elizabeth takes John to watch the Mike's band play at the disco. Jake introduces the band as the Hearts of Sogguth. Mike plays the drum to the special rhythm, everyone in the room is affected, including John, but not Elizabeth. She jaunts onto the stage and stops Mike. When she gets back to John he is acting very strangely. She jaunts back to the Lab and tell Tim that she thinks that John and Mike are under someone's control.

Jake told John that he should stop Elizabeth telling anyone what happened, he gave John a knife. John jaunted back to the Lab and tried to kill Elizabeth, but his instinct not to kill broke Jake's control over him. Mike went with Jake to the Hearts of Sogguth headquarters. During a ceremony a voice warned Jake that Mike was different. Elizabeth found an old book that said that Lord Sogguth would return when a million people hear the beat of his heart, he would then return and destroy the Lords of the Heavens. She thought that the television broadcast would reach more than a million and the lords of heaven could be the Galactic Trig. Tim said that they could not completely dismiss the possibility. The Hearts of Sogguth had captured Mike and held him down, something came out of the sacred drum and took control of Mike. John and Elizabeth contacted Mike telepathically, he lied to them and said he was at home, he also told them that the television programmed was the next day. John and Elizabeth jaunted to the Hearts of Sogguth headquarters to try to destroy the drum. Jake discovered them and made John attack Elizabeth. Jake tried to stab Elizabeth, but she jaunted back to the Lab. The next day Elizabeth jaunted to the television studio just before the broadcast. John told Jake that Elizabeth had arrived, and persuaded Jake to let him search for her, and stop her with a stun gun. Elizabeth was in the gantry and had a laser blaster to destroy the drum. John stopped her before she could fire. Mike started to play the drum, and release Lord Sogguth. John stopped chasing Elizabeth and she got a chance to fire at the drum. Sogguth had been defeated, as he retreated back to the centre of the Earth he took Jake's "soul" with him, leaving his skeleton.