The H.M. Fishery Protection cruiser 'Marlin' is ordered to the Brannan Sound to collect ballot boxes from offshore Scottish islands. Chief Officer Carrick soon realises that Brannan Sound has earned its reputation as a place of fear, where ancient superstitions come readily to life and where a woman know as the Witch of the Isles is a power to be reckoned with. It is not long before Carrick also discovers that the by-elecitons' by-products are not only votes but also terror, sabotage and murder.
