A newspaper article about a vandalized painting catches the eye of William James Moriarty. Recognizing the artist from his childhood days in the slums, he takes his brother Louis with him on a trip to the city of Bath to meet with the artist personally and identify the culprit. However, the person claiming to be the painter is not the man William remembers. Joined by Sherlock Holmes and John H. Watson, William looks for clues in order to find his old friend.

The Moriarty household faces its biggest crisis to date: hosting a tea party. Mysterious and closed off to the public, the Moriarty home hides an abundance of weapons, research, and other tools used in their underground activities. To keep their secret safe from overly curious—and completely smitten—aristocratic women, the entire team must maximize their skills and protect their base of operations at all costs.