The TARDIS arrives on a planet, with the Doctor convinced that this is not his usual error in plotting course, but rather the work of the Time Lords sending him to get involved in something that they themselves want dealt with but don't want to sully their hands with. His suspicions are soon enough confirmed correct, as the plant is home to the Sisterhood (who are the other group who share the secret of the Elixir of Life with the Time Lords), and Solon – a scientist working to return the consciousness of cast-out Time Lord Morbius into a new body.
Although there are elements of this serial that I think did not work particularly well, the vast majority of it is enjoyable for what it is. This is essentially an adoption of Frankenstein and Gothic horror put into the family-friend sci-fi setting. In this regard it is quite fun, and has solidly hammy performances which match the tone – and of course a lumbering and quite unsettling creation of a creature that Morbius will end up inside. Some of the narrative details don't really fit together, and I preferred the bits of the serial that dealt with Morbius more than those focused on the Sisterhood, but mostly it works. The idea of the disembodied consciousness is nicely done, and the design of the creature is good too. Okay, it does end up with the familiar slowly lumbering beast from which to escape, but it is pretty intimidating and while I don't agree with Mary Whitehouse's view on it, it is nicely meaty as a horror for younger viewers.