In my opinion, the best serial in this Key to Time series. The locations are beautifully recorded on tape instead of film, which I think makes them look even richer. The supernatural/horror elements of the story are the best since the Holmes/Hinchcliffe days. Most notably, the two primary guest roles are both played by women...Susan Engel in what could be called a dual role, and Beatrix Lehmann who nearly single-handedly steals the entire show as Professor Rumford. Tom and Mary are particularly good in this one too, and the silly humor is completely absent.
Definitely a high point of the year and one of my all-time favorites of the Fourth Doctor's era.
