Doctor Who loses control of his TARDIS yet again. You might think that this happens so regularly that the Time Lords would revoke his TARDIS driving licence, but it is, of course, a necessary plot device. The whole idea of the programme is that the Doctor and his companions travel round the galaxy having adventures which invariably involve them facing deadly perils; nobody would want to watch a serial in which the Doctor and Sarah Jane spend a relaxing long weekend on a peaceful, danger-free planet. But why would the Doctor voluntarily travel to a place where someone or something wants to kill him? So a means had to be found to get him there involuntarily.
And in "The Brain of Morbius" the Doctor has an excuse for ending up in a place in which he would rather not be, in this case the planet Karn. The TARDIS goes off course not because of mechanical failure or incompetent piloting but because it has been dragged there by some mysterious force. And Karn is certainly a place in which the Doctor would rather not be. He faces danger from two sources. Mehendri Solon, a brilliant but unscrupulous neuro-surgeon, is trying to create a body for the executed Time Lord war criminal Morbius, and needs the Doctor's head to complete his work. (Morbius's brain somehow survived his execution and now continues to exist in a disembodied form in Solon's laboratory).
The second source of danger is the Sisterhood of Karn, an all-female religious cult who worship a Sacred Flame which is the source of their Elixir of Life which guarantees their immortality. They have always had an uneasy relationship with the Time Lords and believe that the Doctor has been sent to steal the precious Elixir.
In the early days of "Doctor Who" in the sixties, the programme tended to be very male dominated. Not only was the Doctor male, so were virtually all his enemies and associates; he fought against cybermen but never cyberwomen. About the only important female characters were some of the Doctor's companions- in those days he also had several male ones- and they tended to be passive figures. During the era of the Third and Fourth Doctors in the seventies, however, there seemed to be a conscious attempt to address the programme's gender balance. The Doctor now nearly always had a female companion; throughout the decade he only had one male one, Harry Sullivan. These female companions could still be young and attractive, but they also had to be shown as intelligent, brave and resourceful and had to play an active part in the Doctor's adventures, as Sarah Jane is shown doing here. The Sisterhood can also be seen as part of this process to create not just female companions for the Doctor but female adversaries as well. It should be noted, however, that the Sisterhood are not portrayed as evil, unlike Solon and Morbius; their dispute with the Time Lords has arisen through a misunderstanding, not ill-will on either part. The vogue for female villains, such as Kate O'Mara's Rani and Jacqueline Pearce's Chessene, was to come later.
The plot of "The Brain of Morbius" borrows from Mary Shelley's novel "Frankenstein", and perhaps even more from its film and television adaptations. Solon's laboratory with its array of weird-looking equipment clearly marks him out as the classical "mad scientist", and his powerfully built but simple-minded servant Condo was clearly based upon Frankenstein's assistant Igor, a character who did not appear in Shelley's novel but who has appeared in many films. An earlier serial in the 13th season, "Planet of Evil", borrows equally heavily from another Gothic novel, Stevenson's "Doctor Jekyll and Mr Hyde".
There is an excellent contribution from Philip Madoc as Solon; Madoc had already appeared in two earlier adventures and would later appear in a third, "The Power of Kroll". Tom Baker and Elisabeth Sladen as Sarah Jane are as reliable as they usually were. The serial also raises some philosophical points such as an interesting debate between the Doctor and the Sisterhood about the advantages and disadvantages of immortality. (The script was officially credited to Robin Bland, a pseudonym Terrance Dicks, but there was a large input from Robert Holmes, who often tried to introduce some of his own political and ethical ideas into the programme). When I reviewed "Planet of Evil" I called it one of the more original, thought-provoking adventures in the series, and I think that the same holds true for "The Brain of Morbius".