A Concorde loaded with passengers and crew vanishes into thin air. The still-grieving TARDIS crew arrive at Heathrow Airport in 1981 as the Doctor volunteers his services to solve the mystery.

The Doctor's TARDIS is stolen, and tracking it down reveals the existence of an alien named Kalid controlling events in the past. While the Doctor challenges Kalid's motives for being there, Tegan and Nyssa discover the source of Kalid's power - an even greater threat for the Doctor.

From within their sarcophagus, the gestalt Xeraphin are communicating through Nyssa. But their psychic energy is so powerful it may destroy her body completely.

The Master's TARDIS is repaired and the Doctor must follow him back to 20th century Heathrow, once he has rescued all the passengers and crew from both Concordes.

The Doctor discovers a starship trapped in a time warp over Earth. Meanwhile, public schoolboy - and secret alien émigré, Turlough, learns he can have that which he most desires, in return for the murder of the Doctor...

The TARDIS lands on Earth six years out of date, stranding the Doctor in 1983 while leaving Tegan and Nyssa to look for him in 1977. Both parties also encounter former companion, Brigadier Lethbridge-Stewart, though curiously, he has no memory of the Doctor at all.

Mawdryn and his eternal mutants reveal the truth: they are exiles, they are in pain and need the Doctor's future 'lives', as afforded by each of his remaining regenerations.

As the Doctor's ethics are challenged and the two Brigadiers finally meet, Turlough plots with the Black Guardian to bring the Time Lord down once and for all...

Lanzarote, 1985. Archaeologist Howard Foster raises a strange metal artefact from the sea floor. But how is it linked to the signal the TARDIS received? Why is Turlough suddenly so worried? And why is Kamelion acting so erratically?

While the Master, victim of his own attempt to improve his TCE weapon, seeks restoration through Sarn's numismaton gas, the truth of Turlough's past comes out at last, though to guarantee the safety of his brother and the Sarn people, Turlough must consider a great personal sacrifice.

Sarn prophesy foretells of an outsider who will come to aid the people. It's a role the Master is more than delighted to fill, which finally presents Timanov, the Sarn religious leader, the unbridled support he's sought in his campaign to cull the faithless from among his people. Turlough's secret past, however, is somehow intricately involved in all this, and the reluctance of its disclosure is enough to threaten all friendly ties with the Doctor.

While the Master, victim of his own attempt to improve his TCE weapon, seeks restoration through Sarn's numismaton gas, the truth of Turlough's past comes out at last, though to guarantee the safety of his brother and the Sarn people, Turlough must consider a great personal sacrifice.