Colonel Flynn O'Flynn (Lee Marvin), a hard-drinking American, manipulates British aristocrat Sebastian Oldsmith (Roger Moore) into helping poach ivory in Tanganyika, which is part of the German-controlled pre-World War I territory of German East Africa. On hearing news that the American has returned, Herman Fleischer, the local German Commander of the Southern Provinces, relentlessly hunts O'Flynn with his Schutztruppen.
Later Sebastian meets and falls in love with O'Flynn's daughter, Rosa (Barbara Parkins). They are married and have a daughter together. Meanwhile the poaching continues. Fleischer has a warship ram and sink O'Flynn's Arab dhow (ship) containing poached ivory. But whilst attacking O'Flynn's home, Schutztruppe under Fleischer's command kill Sebastian's daughter Maria.
O'Flynn and Sebastian decide to go and kill Fleischer as revenge for the death of the little girl. But when it is discovered that Britain is at war with Germany, allied officers convince O'Flynn to locate and destroy the German warship awaiting repair.
O'Flynn, Sebastian, and Rosa pursue Fleischer, who also happens to be on the warship. Eventually they find her in an inlet and sink her.
Who else pursued Fleischer with Sebastian and Rosa?
O'Flynn