When unpopular Captain Sewell is found battered in his cabin aboard The Hakota, an old cargo ship, Felix Dunn takes command. Photographs are taken before a burial at sea and on arrival back in the UK, all leave is cancelled whilst the police investigate. It seems the 'upright' Captain had some diamonds on board - and they are missing. Suspicion soon falls on Dunn. His estranged wife has been overspending - and he has been in trouble before. But attractive DC Helen Ryan, sent in to investigate, believes he is not their man and is prepared to go some way to find out the truth.