Stolen letters lead Sherlock into conflict with Charles Augustus Magnussen, "the Napoleon of blackmail" who knows the personal weakness of every person of importance in the Western world. During the investigation Sherlock is shot and nearly killed by someone who is being blackmailed by Magnussen. Sherlock and John discover the blackmail files in a seemingly impenetrable location.
The title is based on Doyle's short story His Last Bow, whereas the plot contains elements of another short story, The Adventure of Charles Augustus Milverton.