Harrington will play Michael, a fellow addict in recovery, who once found the inspiration to stay sober in Sherlock’s words at N.A. meetings in the past. Michael now offers to return the favor and be an ongoing support to Sherlock, as Season 6 finds Sherlock in a time of need. It was becoming apparent in the Season 5 finale that Sherlock and Joan Watson’s relationship was already feeling some strain.
Harrington played Det. Joey Quinn on all eight seasons of Dexter. He previously recurred as Jack Bass on Gossip Girl, played Alan Shepard on The Astronaut Wives Club and most recently recurred on Shooter and guest-starred on Sneaky Pete and Brooklyn Nine-Nine.