A familiar face returns to Firehouse 51 to serve with Kidd on a special task force. With Tony close to breaking the CFD's perfect attendance record, Mouch and Capp work to keep him safe. Old grudges resurface when Gallo reunites with a family member.
A seemingly simple mold inspection at S.T.A.R. Labs leads to unexpected time anomalies. Barry and Iris try to make sense of the confusion — and figure out how to get back to their reality. Chester admits a secret to Allegra, which makes things awkward between the two, and Allegra relies on Cecile to act as a buffer. Meanwhile, Khione meets with an old friend of Team Flash.
Jimmy challenges Tonight Show audience members to answer random trivia questions in Tonight Show Audience Trivia Night before catching up with Matt Damon and Cecily Strong and welcoming musical guest Rema.