Staying Alive - Sherlock (BBC)

Only four people know of the true state Sherlock Holmes was in just before he met John Watson. The darkness, the drugs, the voices, her. You could argue that her death triggered it. Now that John has left Sherlock to live with his wife it is inevitable that Sherlock will go back to how he was. Until somebody knocks on his door. He wasn't the only one to fake his death. (Set in between TSoT and HLV)