A horse wanders from a town to the countryside. Here lives Sten Stensson Stéen, a bachelor at law and philosophy. He is writing a social psychological report on the youth-problem. In the neighbourhood is experimental school Fridhem situated. The neighbours live in fear of school-boys' pranks and behaviour. The principal of Fridhem resigns. The school risks being shut down. Stéen signs up as a candidate for the vacant service as the principal. The boys welcome him with clever pranks. He fends off and attempts to transform the boys into well-behaved angels.