The Doctor and Jo investigate strange disappearances in the sea that are eventually linked to the Master's plot to use Sea Devils to exterminate the human race.

The writing is clunky and juvenile. For example: "The Judges had decided to sentence the Master to life-long imprisonment. They did not realise that, in the case of a Time Lord, 'life-long' might mean a thousand years!" The science is terrible. The background characters are stereotypes. The plot is slapdash and poorly paced. But nostalgia is a powerful force, and I love the Third Doctor and Jo Grant, so this gets two whole stars from me! ( )

http://nhw.livejournal.com/1037395.html#cutid3

This disappointed me. We start with quite a tedious aside on why the Doctor and the Brigadier intervened to prevent the Master from being executed (after his arrest in The Dæmons), and then we lose some of the more attractive bits of the original story - the quiet feminism of WRN Blythe, the excellent incidental music, and the Clangers. The plot holes, as so often, seem more apparent on the page than on screen. ( )