Oorspronkelijke titel: De liefdesavonturen van Mr. Nicolas, of Het menselijk hart ontsluierd (bewerkt door Henri Borel 's-Gravenhage : Kruseman, 1926) Autobiografie Monsieur Nicolas, ou le Cœur humain dévoilé .
One rainy night a canal worker stumbles across the strangled body of Mary Lampson in a stable near Lock 14. The dead woman's husband seems unmoved by her death and is curt and unhelpful when Maigret interviews him aboard his yacht. But gradually Maigret is able to piece together their story--a sordid tale of whiskey-fueled orgies and nomadic life on the canals. Can the answer to this crime be found aboard the yacht? Or is the murderer among the bargemen, carters, and lockkeepers who work the canal?