When you watch Elementary Season 4 Episode 18 online, Sherlock and Joan are hired to find a missing doctor who was accused of getting a young man hooked on prescription drugs. Initially, the duo investigates the doctor's apparent involvement with a drug-dealing gang that may have been buying drugs from him, though their sights soon turn towards another curious characteristic of the wayward doctor. It turns out that he was a devoted "prepper;" a survivalist preparing against a hypothetical Doomsday. Their investigation takes a grim turn when the missing doctor turns up dead, having been struck by a survivalist's multi-use tool. They begin to wonder if the man's death had any connection with something called "The Keep," on which he spent $100,000. Meanwhile, Sherlock must deal with his own issues as his relationship with Fiona takes a turn. He also complains about the next door neighbor having noisy coital encounters. What will Sherlock do with his relationship? Will it grow and develop, or is it doomed to end prematurely? Who killed the doomsday-prepping doctor, and why? And where was he actually killed? Find out the answers when you watch Elementary Season 4 Episode 18 online!