The two policemen had, instead of obeying their orders to arrest a suspect at Arlanda Airport, been arguing with a man whose 3-year-old son had shouted "Police, police, mashed potatoes" at the two policemen while they were eating hot dog with mashed potatoes at a grill bar.

Martin Beck has to search through the high powered business man Viktor Palmgren's many enemies when the business man is shot in front of a dozen witnesses at a high-end restaurant.

Behind the facade of legal transactions he finds out that Palmgren had earned most of his money with illegal arms deals.

Svensson confesses and is arrested while Palmgren's unscrupulous business partners remain largely undisturbed.

The 1979 Latvian film Unfinished Supper, directed by Jānis Streičs, was based on the book.