While doing research in the hospital morgue, Sherlock stumbles upon a murder that everyone else overlooked. According to Holmes' deductions, someone in the hospital has been killing weak and terminal patients and making it look like they had died of natural causes. While interrogating hospital doctors and staff, the evidence begins to mount--Sherlock is chasing an angel of death.
Watson reconnects with an old doctor friend of hers while working with Sherlock at the hospital. While sitting in on a pre-op procedure, she learns that Sherlock is not the only one with an uncanny sense of intuition.