Twelve year old 'Boefje' spends most of his time in the alleys, on rooftops and in the harbor of Rotterdam. A local clergyman takes pity on him and attempts to teach him good manners.

When Erica Maerlant is shot dead during a secret dance rehearsal at her luxurious villa, the Maerlant household turns out to be a serpent's nest of intrigue where everyone has a motive for the murder.

Circus artists Jan and Annie are in possession of jewels that were - unbeknownst to them - stolen from the famous Jolly Sisters. Mistaking them for the thieves, two bumbling detectives infiltrate the Dutch theatre-life.