In 1930s Amsterdam, greengrocer Bet is involved in illicit affairs with businessman Van Santen. To tighten bonds even further, Bet arranges a marriage between her handsome daughter Jans and the businessman's wacky son Hannes. Jans, however, is in love with tough sailor Ko. Based on the succesful Dutch stage musical by Herman Bouber.

Unaware of its contents, kind-hearted captain Beets delivers a package containing smuggled diamonds to Balthazar, the far from honest owner of an Amsterdam dance-hall. To double his profit, Balthazar shoots the innocent captain in cold blood and makes it appear as if Beets has committed suicide. The captain's daughter Eva and her sweetheart, young author Willy Vermeer, see through Balthazar's plans and will not rest until the criminal is punished for his deed.