The Doctor has begun his exile on Earth–reluctantly. The Time Lords have removed key components from his TARDIS and blocked memories necessary to fixing it. Until he can develop a workaround, The Doctor has agreed to work with Brigadier Lethbridge-Stewart and UNIT, last seen in “The Invasion.” Assisting him is Liz Shaw, initially skeptic about alien life, her adventures with UNIT expose her to a larger, stranger world.
A new foe, The Master, arrives on Earth, and the Doctor gets a new assistant–the whimsical Jo Grant. UNIT faces new foes from outer space while also dealing with ancient evils buried at Devil’s End.
The Doctor, Jo, and UNIT face Daleks, a new colony of Silurians, and a dangerous time experiment. In between, the Time Lords send the Doctor on a mission to the planet Peladon and the Earth Empire in the 30th century. The Doctor must figure out what the Time Lords want before he can return home.
When Gallifrey is threatened by an ancient Time Lord, The Doctor is united with his First and Second incarnations to prevent the destruction of the universe. In gratitude for his efforts, the Time Lords restore his memories and repair his TARDIS. Exercising his new freedom, the Doctor and Jo stop intergalactic con artists, Daleks, and prevent a war between humans and Draconians. Jo Grant departs, desiring to make a difference on Earth with her new fiance Professor Clifford Jones.
Scientists are disappearing and journalist Sarah Jane Smith investigates, believing UNIT and the mysterious Doctor know more than they are telling. After defeating a Sontaran plot in medieval England, the Doctor and Sarah return to a London plagued by dinosaurs. Sufficiently intrigued by the Doctor and his adventures, Sarah joins him on trips to Exxilon and Peladon. The Doctor faces death, however, when Mike Yates brings news of strange happenings at a meditation retreat.