But Chris escapes, locking the policemen and Robert's grandfather in the cellar. Robert reveals to John that he is an alien Denagelee, but was born on Earth from an egg. When hatching, his species require aggressive energy to complete the transformation; the destruction of the Roman Empire was caused when his mother hatched - this time there will be many thousand of his race hatching. John persuades Robert to release him, so that the Tomorrow People can try to find a safe way for the aliens to hatch. As the hatching begins, Stephen suggests that if they could use a giant stun gun in space to put everyone to sleep - their REM state could provide the energy needed by the Denagelee, without hurting anyone. John, Stephen and Elizabeth collect the parts needed for the gun, and take them to the Watchdog satellite to assemble. Once activated, the stun gun sends everyone to sleep, allowing them to dream the violence the Denagelee require. The aliens leave Earth, agreeing never to return. John, Stephen and Elizabeth return home, and Stephen erases the memories of the policemen, who set Chris free. (thetvdb.com)