Commissioner Borowski is on his way home from a fishing holiday when he is called for help at an unusual point: in the middle of the sea, on the way from Sweden to Germany, the captain of the ferry has disappeared without a trace. Borowski had seen him shortly before, when Captain Venske had been arguing with his First Officer Björndahl at the bar. Borowski has all the passengers on the ferry screened and reconstructs the captain's last hours. Even the first trace is strange: someone has opened the pilot door - the signal for an emergency. Did Captain Venske leave voluntarily, was it suicide, accident or murder?