Recovering addict Tommy Jarret has rented a chalet to check out reports of a sea monster near the village of Drim. Then he turns up dead, apparently from a drug overdose, and constable Hamish Macbeth finds the lad's demise particularly fishy. Deciding to go undercover, Hamish infiltrates the local drug dealing trade. But his plans looks doomed when he's teamed up with a tough Glaswegian detective inspector named Olivia Chater, aka Concrete Knickers. For the Lochdubh lawman it would be equally dangerous to flounder ... or fall in love.