The case surrounds the bizarre theft and apparently wanton destruction of three plaster-cast busts of Napoleon; one at a shop in Kennington owned by Morse Hudson (who, according to some Holmesians, is the estranged husband of landlady Mrs. Hudson), and two others at nearby addresses in south London. Lestrade’s idea that the thief could be a “criminal or lunatic,” and possibly a “local fanatic,” perhaps stems from the area’s close proximity to Bedlam, the notorious insane asylum—now London’s Imperial War Museum. In any case, this theory serves Holmes well. When a fourth bust is stolen from the home of Horace Harker, a journalist in Kensington, and a man is found murdered on the front steps, Holmes’s false hint to the resident journalist about “a dangerous homicidal lunatic, with Napoleonic delusions” is reported in the evening papers. Chuckling over the reports later on, Holmes remarks, “The Press, Watson, is a most valuable institution, if you only know how to use it.”

It is clear that Holmes has a plan: while these reports are designed to mislead the criminal and make him think that Holmes is clueless, in fact he has two major leads. One is a photograph carried by the murder victim, depicting “an alert, sharp-featured simian man, with thick eyebrows and a very peculiar projection of the lower part of the face, like the muzzle of a baboon.” This description accords with phrenological theories about criminals’ physical appearance.

The other clue of interest to Holmes is that before smashing the fourth bust, the thief had mysteriously carried it from the house to a better-lit place farther down the street, even though he risked being seen while doing so. If this was merely an act of destruction, why did the thief need to do it in the light?

In typical Scotland Yard fashion, Lestrade focuses only on the murder and the break-ins. Unlike Holmes, he doesn’t see that the Napoleon busts are the key to the case. Holmes traces the busts back to the workshop where they were made in Stepney—a district that was described as “vicious, semi-criminal” by social researcher and philanthropist Charles Booth, and characterized by Conan Doyle as a place where “tenement houses swelter and reek with the outcasts of Europe.” Here Holmes discovers that the photographed man is Beppo, an Italian former employee, who had been jailed the year before for knifing a man in the street, at around the same time the busts were made. At 221B that evening, Lestrade identifies the murder victim as Pietro Venucci, a mafioso from London’s squalid Italian underworld. Now interested in the busts, Lestrade’s new theory is that Venucci was sent to kill the bust-smasher, in some kind of mafioso vendetta. However, Holmes knows better, and offers him a bet that they will catch the villain that night at the Chiswick home of Josiah Brown, who purchased one of the two remaining busts out of the six the workshop had produced.

Beppo is duly arrested at Brown’s house and Lestrade sees the case as closed, until Holmes offers to explain the full facts the following evening at 221B. Purchasing the last Napoleon bust from its new owner for a seemingly generous £10, he promptly smashes it, thus revealing that hidden inside is the priceless “black pearl of the Borgias,” the most famous pearl in the world, which had previously been stolen from an Italian hotel room. Holmes cannot claim all the glory, since Lestrade’s work was vital for this theatrical climax. Holmes realized what was afoot when he learned the name of the murder victim, Venucci. Remembering the theft of that pearl the year before, he recalled that the suspect, a hotel maid, had the same surname. She had passed the stolen pearl on to her brother, who had been stabbed and robbed by Beppo during a street fight. Before his arrest for the stabbing, Beppo had hidden the pearl inside an unfinished bust at the workshop. Venucci had been looking for Beppo when he stabbed him outside Harker’s house.

Lestrade’s heartfelt praise—“at Scotland Yard… we are very proud of you”—elicits a rare glimpse into Holmes’s sensitive side, and Watson observes how “he was more nearly moved by the softer human emotions than I had ever seen him.”

Inspired by “The Six Napoleons”, The Pearl of Death was a 1944 film starring Basil Rathbone and Nigel Bruce, in their ninth outing on screen as Holmes and Watson.