Scottish noble Sir Aaron Armstrong is a reformed alcoholic who advocates temperance and hires dipsomaniac Patrick Royce as his secretary on condition he give up the sauce. When Armstrong learns that his daughter Alice plans to marry Royce, he ignores Royce's fifteen months of sobriety and discharges him. Not long after, Armstrong is found with a broken neck outside a high window on his estate, the apparent victim of foul play. Father Brown assists Inspector Gilder in investigation.