Sherlock and Joan investigate the murder of a young woman and tie her to a billionaire technology CEO. They are shocked to discover that the victim is the CEO's illegitimate daughter, and that the CEO is in poor health after receiving a heart transplant. Joan questions the CEO's wife who reveals that the victim was donating blood to her father and was recently included in his will. Questioning the victim's on-again-off-again boyfriend leads to the discovery that the victim was ill and Joan realizes that the actual target was the CEO, who dies during the investigation. Sherlock and Joan corner the wife into admitting that she was using the daughter as an incubator for the antibodies used to destroy the CEO's new heart and kill him. Meanwhile, Mycroft tries to convince Sherlock to return to London saying that their father is disappointed he hasn't returned to his work at Scotland Yard. Mycroft is lying to Sherlock.