A dying French naval frigate captain tries to make a last rendezvous in the winter storm-tossed seas off the Grand Banks, with "le crab tambour," a French war hero he had betrayed twenty years earlier. "Le crab tambour" the drummer crab" was a boyhood nickname for the handsome young Alsatian whom the film depicts proving his courage, first in the war in French Indochina, and then again in the "Generals' Revolt" in Algeria. Courtmartialed because friends like the French naval captain were afraid to risk their own careers by testifying for him, the exiled "crab tambour" and his trawler, The Shamrock, is now a legend among the Grand Banks fishermen.
Tintin is informed by the Thompsons of a case involving the ramblings of a drunken man, Kelber, later killed, found with a scrap of paper from what appears to be a tin of crab-meat with the word Karaboudjan scrawled on it. His subsequent investigation and the kidnapping of a Japanese man interested in talking to him leads Tintin to a ship also called the Karaboudjan.