Sherlock gets a call from Scotland Yard about a missing inspector, Lestrade, that worked with Sherlock. Sherlock and Joan go to London. Sherlock easily locates Lestrade at a bar and agrees to help solve the case that caused Lestrade to be suspended. Attempting to prove a rich man killed his wife, Sherlock, Joan, and Lestrade pour over evidence. Refrigerated milk leads them to visit the suspect's house where Sherlock discovers a chipped nail, leading him to the conclusion that the gun was printed using plastic and melted in acetone. Tracking 3D printer purchases leads them to the body of the suspect's handyman, and plastic fragments found on the scene prove Sherlock's hypothesis that the man printed a gun to kill his wife and killed the handyman to clean up loose ends. Meanwhile, Sherlock is shocked to discover his brother, Mycroft, has moved into his old place at 221B Baker Street. Mycroft is interested in how Joan became Sherlock's friend and reveals he wants to make amends with Sherlock. Mycroft uses a homemade bomb to destroy Sherlock's belongings (and get his attention).
