During the holidays, the Flash confronts the Reverse-Flash, the man who killed his mother. Caitlin gets surprising news about her fiancé, Ronnie.
While enjoying holiday traditions with friends and family, sudden news from Iris and Eddie startles Barry. Also, another visit from Barry's arch nemesis (the man who murdered his mother) has everyone starting to realize who they're up against. While much is learned about The Man in the Yellow Suit, a former Star Labs employee also appears, one well-known to the group of friends.
Merry Christmas! Well, at least for everyone except Barry. When a "Yellow Blur" attacks a research facility, Barry is forced to become the Flash and find "Opposite Flash" (blame Cisco). Meanwhile, Caitlyn and Cisco go on a personal mission.