William Horatio Ambrose (Guinness) wants desperately to live up to the proud family tradition; the Ambroses have always been mariners (even if not distinguished ones), hence their family motto, ""Omnes per Mare"" ("All at Sea"). In humorous vignettes, Guinness portrays six of his ancestors, starting with a confused caveman perpetually going in circles in his coracle, and ending with his own father's ignominious demise at the Battle of Jutland. Ambrose has a debilitating problem however: he suffers from violent seasickness. As a result, his contribution to the Second World War consists of testing cures for the malady.