I don't always agree when people say a story has 'palpable atmosphere' but this is a prime example of that. Dark, brooding, horrible, unsettling. It's structure is all jumbled up, but it uses that to build up to a horrifying realization, something even the doctor doesn't realize, or if he does, he makes sure that Nyssa doesn't find out. It's a highly affecting story that feels half-formed on purpose, stylistic and conceptual, and it really pulls it off.
10/10