Normally, the overdose death of a heroin addict would hardly raise police suspicions, but our favorite Scottish constable, Hamish Macbeth, is unlike most police and he wonders about more than a few incongruities. And what does it all have to do with new sightings of another monster in the local loch. Hamish suspects nothing more than a new family of seals. In order to collect more information about the heroin overdose, Hamish, with the surprise approval of his Strathbone superiors, goes undercover, literally and figuratively with a notorious detective inspector posing as his wife. Those knowing Hamish will recognize the scenario for trouble and sure enough. But the real trouble is caused by that pesky detective inspector Blair, who remains so envious of Hamish's local success.