博士和新同伴Leela继续在时间与空间中遨游，他们来到了一座灯塔流传着一个传说；压榨人的税收星球；在回到母星后，博士似乎怀揣着一个邪恶的秘密…

维基：

Philip Hinchcliffe era
The planet Karn is home both to a mystic Sisterhood, whose sacred flame produces an elixir of life, and to Mehendri Solon, a fanatical scientist who is using the remnants of spaceship crash victims to put together a new body for the still-living brain of the executed Time Lord criminal Morbius.
When the Doctor and Sarah arrive on the planet, Solon decides that the Doctor's head is just what he needs to complete his work. The Sisterhood meanwhile fear that the Doctor has been sent by the Time Lords to steal the last drops of elixir produced by the dying flame. They kidnap him and plan to burn him at the stake but he is rescued by Sarah, who is temporarily blinded in the process.
The Doctor is tricked by Solon into believing that his companion's condition is permanent. He asks the Sisterhood for help and restores their sacred flame to its former glory using a firework to clear its blocked chimney. Returning to Solon's citadel, the Doctor and Sarah become trapped in the cellar.
The Doctor releases cyanide fumes into the ventilation system and Solon is killed, but not before he has used an artificial brain case to complete Morbius's new body. The now-mobile Morbius accepts the Doctor's challenge to a mind-bending contest, which takes a heavy toll on both of them. The Sisters force the crazed Morbius over a cliff and he falls to his death. They then use the elixir to heal the Doctor.

This season introduced K9 to the series and saw the departure of Leela. It was originally intended to include Terrance Dicks' story The Vampire Mutations but, due to a major BBC production of Dracula, it was postponed. It later became Season 18's State of Decay. To replace it, Dicks quickly scripted the season opener, Horror of Fang Rock. The season took a two week transmission break over the 1977 Christmas period, between the broadcast of part four of The Sun Makers and part one of Underworld.

Can the Doctor, now in his fourth incarnation, recover from his post-regenerative trauma to save the m.youlady.cc Earth from Think Tank and their plot for world domination?

The Doctor's past incarnations are taken out of time by a forbidden time scoop device. The fourth Doctor becomes trapped in the vortex but the others find themselves, together with a number of their old companions, with the fifth Doctor and his companions in the Death Zone on their home planet Gallifrey.
Here they face a Dalek, a Yeti, a quicksilver Raston Warrior Robot and numerous Cybermen. Also present is the Master, who has been summoned by the High Council of Time Lords to help the Doctor. It turns out that President Borusa is the mysterious operator of the time scoop. He aims to use the Doctors to breach the defences of the Dark Tower - Rassilon's tomb - so that he can enter there and claim immortality.
When he does so, however, he is condemned by Rassilon to eternal existence in the form of a living statue.

维基：