Liam Danow is an ex-boyfriend of Joan Watson. He was arrested on a hit-and run-charge, asked for Joan's help and after initially refusing to lend him a hand, was cleared by Joan. Joan was reluctant to help him at first because he had betrayed her trust before. He was her first experience with addicts, and his repeated using and relapse inspired her to get a job as a sober companion. It also made her wary of emotional entanglements with addicts, which still colours her interactions with Sherlock. As of the end of season 4, Liam has been seen only once.