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?

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.

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.

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.