The Flash (2014): Season 3, Episode 12

3 - 12: Untouchable

Barry and the team at S.T.A.R. Labs work together to bring down Clive Yorkin, a criminal meta-human who is methodically killing people by causing them to decompose at an accelerated rate. Joe becomes his next target but it's Iris who is caught in the crossfire. The Flash mentors Kid Flash and begins to elevate the newer speedster's training to another level.