When a body is found in Holmes's 221B Baker Street lodgings on the set at Mammoth Studios during the shooting of The Valley of Fear, Groucho and his sidekick Frank Denby begin investigating. The victim is the German emigre director of the movie who was found in the great detective's favorite armchair, stabbed in the chest with Holmes's pearl-handled letter opener. There is another murder but it takes more than murder to stifle Groucho's quips or to quiet the laughter this surprising reincarnation inspires.