Recovering addict Tommy Jarret rented a chalet to check on reports of a sea monster near the dour village of Drim. When he turns up dead, apparently of a drug overdose, Lochdubh constable Hamish Macbeth finds the lad's demise to be particularly fishy - and not of the local salmon variety. Hamish decides to infiltrate the illicit drug trade in nearby Strathbane, but his daft scheme springs a leak.