Summary : Arsène Lupin, gentleman-cambrioleur

The transatlantic steamer La Provence sets off under pleasant conditions, carrying a distinguished group of passengers across the ocean. Among them is Miss Nelly Underdown, a wealthy and beautiful young woman who commands the attention of numerous admirers, including the narrator. Life aboard the ship feels intimate and self-contained until the wireless telegraph transmits an alarming message halfway to their destination: the notorious and elusive master criminal Arsene Lupin is on board traveling first class under an alias starting with the letter R, with blonde hair and a wound on his right forearm. This revelation instantly transforms the atmosphere of the ship into one of suspicion and anxiety. Passengers begin scrutinizing one another, wondering if the infamous gentleman thief is sitting next to them in the dining room or walking the deck. Using the passenger list, the narrator deduces that a reserved, taciturn passenger named Rozaine fits the description. Although Rozaine jokingly plays along and reveals his arm, he shows his left arm instead of the injured right one, deepening the mystery. Soon after, Lady Jerland discovers that her cabin has been broken into and her finest jewels selectively stolen. Suspicion intensely focuses on Rozaine, leading the captain to question him, though he is soon released because his papers are in order and he lacks any physical wound. Rozaine subsequently attempts to clear his name by offering a large reward to anyone who can expose Arsene Lupin, going so far as to actively investigate the passengers himself. Despite rigorous searches of the ship and cabins by both the crew and Rozaine, thefts continue to occur, culminating in the theft of the captain's own watch. The tension among the passengers reaches a fever pitch as nobody feels safe from the seemingly omnipresent criminal. The suspense peaks on the penultimate night when Rozaine is found bound and gagged on the dark deck, robbed of twenty thousand francs. A calling card pinned to his clothing thanks him for the money on behalf of Arsene Lupin, proving conclusively that Rozaine is an innocent victim rather than the mastermind. With Rozaine cleared, panic spreads completely through the vessel. The passengers realize that Lupin could be anyone among them, possessing unlimited disguise and cunning, and they await the remainder of the journey in terror of what final disaster he might orchestrate before reaching port.

During a gathering at the home of Monsieur de Dreux-Soubise, conversation turns to the infamous, unsolved theft of the Queen's Necklace from a century earlier. Among the guests is the Chevalier Floriani, a man acquainted with Sicilian magistracy who casually dissects the locked-room mystery. With chilling precision, Floriani deduces how a small child could have entered through a transom window using improvised tools, identifying the culprit as Raoul, the son of the house's former maid Henriette. The host and guests are left stunned as Floriani methodically proves each point, explaining how the young boy executed the heist to alleviate his mother's financial misery. As the discussion continues, the atmosphere grows tense and ironic, leading the company to realize the startling truth. The Chevalier Floriani is none other than Raoul himself, now grown and boldly confronting his victims with the mastery of a master criminal. Rather than causing a scandal, the humiliated count and countess engage in a tense verbal duel with him regarding the historical necklace and its mount. Impressed and unnerved by his audacity, they are left powerless as the gentleman thief gracefully takes his leave. Four days later, the stolen Queen's Necklace is mysteriously returned to Madame de Dreux-Soubise in a red leather case bearing cardinal arms. Shortly after, a sensational press report credits Arsène Lupin with recovering and returning the historic heirloom to its rightful owners. The narrator reflects on his own strange entanglement with Lupin, recalling a terrifying night when he was held paralyzed in his own bedroom by the mere shadow of a curtain while a burglary took place nearby. Believing he was guarded by an armed intruder, he spent agonizing hours frozen in fear until dawn broke, only to discover he had been terrorized by an empty fold of fabric.