The search for the third segment of the Key to Time takes the Doctor, Romana and K-9 to Earth and a mysterious stone circle where they encounter cultists, vampiric rock and a four millennia old intergalactic criminal.
This was always my favourite story of the Key to Time and certainly the most fun. Every interaction between Professor Amelia Romford and the Doctor or K-9 is fantastic. The novelisation may miss out on the onscreen chemistry between Tom Baker and Beatrix Lehmann, but each bit of witty dialogue is present and Dicks has a good grasp of Romford and the Doctor's relationship.
Being hard to realise onscreen, both the Ogri and the Megara benefit from being novelised. There is also a strong villain in Cessair of Diplos. She possesses both charm and a sense of ancient evil. Her various historical and mythological guises and her great age make her a very interesting opponent for the Doctor.
The use of a stone circle to mix the ancient historical with the science fiction is obviously not that unique (`Children of the Stones' only did it the year before `Stones of Blood' was broadcast) but it is done here exceptionally well and it blends in successfully to the whole Key to Time idea.
The Doctor encounters a group of Druids led by a man named de Vries and narrowly avoids becoming their latest sacrifice. De Vries is later killed by one of the stones from the circle - an Ogri, a life form that lives on blood. Miss Fay is the latest guise of the Cailleach, a being worshipped by the Druids, who has been on Earth for four thousand years. She transports Romana to a spaceship suspended in hyperspace at the same coordinates as the stone circle.