Lieutenant Colonel Brusefjær, a highly regarded "administrative officer" from his time in London, is a man with a keen eye for everything that goes on around him, especially suspicious individuals. But now he wants to relax, and together with his grandson Lille-Bertram and his caretaker Ole Gliset, he mans the houseboat Caroline 11 and travels to Hankø. The police have just received alarming reports of widespread smuggling – probably based in the outer Oslo Fjord – and a trusted investigator, Reidar Nissen, is sent on vacation to Hankø.