Plot construction remains a problem for van de Wetering--the mystery here isn't mysterious--but never before have his strengths seemed so strong: the genuine humor, decency, and wisdom of his Amsterdam policemen positively glow here, crisply juxtaposed with some odd folk in northern, coastal Maine. Why Maine? Because the stupid, helpless sister of Amsterdam's old, arthritic commisaris lives there, and she has just become a widow--so the commisaris must go and help her. And unofficially tagging along, to keep an eye on the commisaris' health, is that curly-haired swinger manquÃ‰, Sergeant de Gier. The Dutchmen soon learn that the commisaris' brother-in-law is only the latest in a string of accidental-death victims along unspoiled Cape Orca. Among the suspects: a bizarre mini-gang of intellectual anarchists (one of whom seduces de Gier) and the educated hermit who owns the island just off the cape. The Maine locales glisten with the cold; the interaction between characters is charged with warmth. Only the ragged plot keeps this from being a thoroughly satisfying mystery by a very special sort of mystery writer.