Donald Lam arrives at work one day to find an outraged police sergeant Frank Sellers stewing in the office of his senior partner, Bertha Cool. Sellers is close to cracking an armoured car robbery case, but in the course of his investigation, a telephone number for the Cool-Lam detective agency was found on one of his primary suspects - one Hazel Downer.

The same Hazel Downer employs Donald Lam to find her husband who has run off with another broad, taking her fifty thousand dollars with him. Wasn't it fifty thousand dollars that haven't been recovered from the armoured car job ... ?