Leela is concerned by the Doctor's strange behaviour when, after a secret meeting with aliens, he returns to Gallifrey and abruptly stakes his claim to the Time Lord presidency.
The Doctor is made president of the Time Lords. He immediately orders K-9 to lower the planet's defences and has Leela banished to the wilderness.
The Doctor has betrayed his own people and enabled a Vardan invasion of Gallifrey. Leela joins forces with the Outsiders and prepares to strike back against the aliens.
As the Vardans finally fully materialise on Gallifrey, the Doctor prepares to spring his trap. But does a more deadly alien force lie behind the Vardans?
The Sontarans have taken control of the Capital on Gallifrey and intend to use the power of the Time Lords to rampage through all of time.
Stor, the Sontaran leader, finally gains access to the TARDIS in search of the Great Key of Rassilon and a dangerous game of hide and seek begins inside the Doctor's ship.