This is part of a series of reviews of Doctor Who in chronological timeline order.

Previous Story: Plague of the Daleks

I quite like the 30-minute story format but sometimes it can lead to stories like this where I feel like there just isn't enough time to really flesh out the story. I'm still not really sure what the point of this one was? I don't feel like the villain was explained very well. Mathematical demons?

I liked that the villains were defeated by an oversight with the Doctor's biology. It was a bit too predictable though and for a monster with such a carefully laid out plan to not even bother checking whether the Doctor or Nyssa were actually human is just silly.

Next Story: The Entropy Composition