Knox's stalwart Webb Carrick--in his twelfth adventure aboard Her Majesty's Fishery Protection Service cruiser Marlin, again plying the waters off the Scottish coast. This time, however, the mystery starts out on a personal note: formidable Capt, Shannon of the Marlin is concerned about the death of his alcoholic old friend Gibby MacNeil, found frozen in the ice-filled fishhold of the Cailinn, docked at Port Ard. So Carrick and Shannon try to find out more about MacNeil's demise--but run into trouble: Capt. Shannon is put out of commission; a dead frogman is found during cave-explorations with local fisherman Jamie Ross; the corpse turns out to be a crewman from a Russian fish-processing ship--a ship whose local Port Ard agent seems a bit shady. And, after a gruesome climax (the explosion of Ross' fishing-boat, killing all on board), Carrick figures things out, forces a confrontation with the chief culprit. . . and, aided by his rugged crew, winds things up with a fast sea-chase/capture. Lots of action, lots of ship-lore, plus a well-observed picture of an isolated fishing community: straightforward entertainment--and just about Knox's best so far.