1. Step Nine

Complete story — includes the ending

Gareth Lestrade, a Scotland Yard inspector who worked with Sherlock, is missing. Sherlock and Joan locate Lestrade at a bar in London and agree to help solve the case that caused him to be suspended. Lestrade accused wealthy Lawrence Pendry of killing his wife, but had no proof. Pendry claimed that an armed intruder shot her; the police arrived within minutes and the gun could not be found. A plastic gun turns out to have been made using a 3D printer; Pendry later dissolved it in acetone in a milk bottle after shooting his wife. Pendry's handyman is later found stabbed to death. Pendry printed a second gun to tie up a loose end. The gun exploded when he fired it because he used the wrong ammunition, so he had to stab the handyman with a knife. Pendry's arm injuries from the explosion secure his arrest. Meanwhile, Sherlock discovers that his brother Mycroft moved into his old apartment at 221B Baker Street. Mycroft tells Joan that he wants to make amends with Sherlock after facing a cancer diagnosis and subsequent bone marrow transplant.