Part 1

The tourists have returned to the Scottish mainland and Inverdee is preparing for the long hard winter. However, Sheila Anderson's late arrival has a dramatic effect on the island community, as Michael Gaffikin and Inspector Inskip are soon to discover.

Part 2

The brutal murder of Sheila Anderson remains a mystery. Could it have been a ritual killing? While her murderer roams free, Inverdee's community is in great danger.

Part 3

Dr. Symonds has been brutally murdered. Radioactivity is discovered on Inverdee; a 'flying saucer' has been sighted, and a strange craft is found on the sea-shore. Are these incidents connected with the recent killings?

Part 4

Although the film from Dr. Symond's camera reveals the presence of a grotesque, monster-like creature, Inspector Inskip remains suspicious of the Colonel's activities.Unknown to the island community, the coastguards are fighting for their lives.