Two patrolling cops stumble on to three criminals who have just stolen large amounts of explosives, and are killed in cold blood. Martin Beck and his team must now work day and night to find out who the killers are and what they are planning to do with the explosives before it's too late. Meanwhile, Gunvald Larsson who was a close friend of one of the murdered cops is ignoring all rules in his quest for revenge.

A boy imprisoned for a double murder is used in a prison experiment involving placing an animal in the cells of prisoners.