1930s, somewhere over the English Channel: a family from Yorkshire is on the 12.30 flight from Croydon to Paris - but by the time the plane lands, Andrew Crowther, a wealthy retired manufacturer, is already dead... Flash back four weeks. Andrew's nephew, Charles Swinburn, is facing the prospect of bankruptcy. In desperation, he devises a cunning scheme to tempt a rich young woman into marriage and dispose of his uncle, thus solving all his financial problems. But all does not go according to plan, and Charles's bad luck is compounded when Inspector French shows up on the scene...