A woman is found executed by hanging at the cinema of a small town in the Swedish forests. The only clue is a math problem, and the town's only commissioner has dyscalculia. The only one who can help her is Ronnie "the Professor", but he can only solve math when he is drunk. However he has recently stopped drinking as he is trying to patch up the relationship with his daughter, who he just met for the first time in 18 years. But the commissioner is very persistent and soon they discover that each new math clue leads them to new victims.
