Otto Carl, with the assistance of two hoodlums, rob the Ajax Manufacturing Company safe of a reported $80,000 and hand-off the plunder to an accomplice driving a home-delivery milk truck. When the milkman, Frank Bonner, disappears with the cash, Otto, having created a fictitious purpose, hires Richard Diamond to find the man. The trail to Bonner begins at the rooming-house that he has called home for three years. The only clue discovered in the room is a swizzle stick from the Purple Grotto nightclub. Although not able to point to any possible location to find Frank, the owner of the nightclub provides a significant revelation. It seems that Otto's wife, Marion, and Frank, once had an intimate relationship. Diamond is now convinced that Marion is the key to resolving this case in short order.
—Harry Tumilson