Monsieur Maurice, onetime gangster and now well-respected owner of the celebrated Sardine Restaurant, is found shot dead on a quiet Montmartre street. Maigret, perplexed by an apparently motiveless crime, enlists the aid of the lugubrious but encyclopedically knowledgeable Inspector Louis in unraveling some of the mysteries of the case; the superintendent soon finds cause to suspect the wifely devotion of Maurice's lovely blonde widow. And he is startled when he sees the priceless antique furniture in her apartment.

The solution of this confusing affair eventually hangs on whether Maigret can trace a mysterious telephone caller with a high-pitched voice before other interested parties can get hold of him.