Sherlock has lost his short-term memory for the last six hours. He has a severed head with no idea where he got it. He and Joan are in the midst of investigating the murder of a theater critic. Sherlock went to tell Captain Gregson about his condition and the severed head. Gregson tells him he has to be cleared by the department's medical office before he could work again. The head John Doe was an organ donor, so Joan and Marcus go to check out the donor of skin used on the dead theater critic. Another skin donor was killed recently in a suspicious fire. Dominic Voth, the president of the tissue banks supplying the donated parts, acted guilty when interviewed by Marcus and Joan and refused to cooperate. That was where Sherlock stole the head. Michael drops by unexpectedly, having tracked down Sherlock. Sherlock tells Michael he has no leads on the missing woman Michael asked him to find. A sample pulled from the first tissue donor indicated a rare strain of bird flu. Marcus figures out the identity of the donor body as Eric Russo. Voth admits he had the donor body embalmed to destroy evidence of contamination. So the body broker becomes their next suspect, but he was out of the country when the murders happened. Michael tells the support group about Sherlock's struggles, and explains he gave Sherlock a project to keep him occupied. Joan comes up with a theory that antibodies in Russo's body could be used in a universal flu vaccine and be worth millions, and someone may have killed him for those antibodies. Dr. Selsky of the Department of Health is their suspect. Marcus found evidence at Selsky's other lab. Gregson lets Sherlock go back to work as long as he continues to go to weekly doctor appointments.