Latin teacher Birger Sjögren at Ringsala boarding school threatens his possesive and chronically ill mother that he will get married. She gets a stroke and dies. Sjögren is affected by feelings of guilt, envy and hatred towards the surroundings. A series of mysterious fires have taken place around the school the last few months. One of the students has seen Sjögren setting fire to a barn. But can he convince the trusted biology teacher Nordmark, expert of the criminal mind?