Police constable Hamish Macbeth is baffled by two apparently unrelated mysteries: a huge quantity of table salt has been stolen from Rory Campbell's general store; and Geordie Robb, a local bully, is missing. Hamish outwits his superiors when he makes a connection between the two mysteries.

Newcomers to Lochdubh Vicky and Paul Jeffreys cause a stir: Vicky tries to put reluctant villagers back in touch with their Highland heritage, gradually alienating them. Hamish investigates when this unpopular, meddling newcomer, receives anonymous threats.

Major Maclean stages a robbery to make a false insurance claim. Before Hamish can settle things quietly, Inspector Bruce instigates a major surveillance operation.

On a mountain trek led by Colonel Don Maxwell, Hamish advises caution once the climbers have reached their goal, but Maxwell urges them on into a dangerous situation.