The episode opens with Harrison Wells running from Zoom in a dream-like sequence, he's in the Breach Room when Zoom grabs him by the throat and holds him up. Wells begs Zoom to let Jesse live, and Zoom puts him down and says "merry Christmas."
At Jitters, Iris brings her father a Flash toy for Christmas, and he feels bad that he doesn't have anything for Barry. He feels a little bad that he never had a son to lavish his attentions on.
At the crime lab, Barry and Patty are making out when Iris walks in on them. Patty goes back to work and Barry starts talking about how happy he is to Iris. She starts to cry, and he wonders what's going on. She tells Barry that her parents had a son that Joe doesn't know about. His name is Wally West.
Barry hugs her and tells her they can tell Joe together and it will be okay. Outside, it begins to snow.
At S.T.A.R., Jay and Caitlin are trying to figure out how to close the breaches and stop Zoom. The two are being so adorable, Cisco makes fun of them -- and then after a bit of comedy where Jay pretends there's no Christmas on Earth-2, Caitlin invites him to a party.
Cisco leaves to go find Wells, but bumps right into him on the way out.
At Iron Heights Prison, a blows in some large windows, and Weather Wizard enters, tossing two guards aside. He brings the weather in with him and uses his powers to free Captain Cold and The Trickster, who has been sitting in his cell obsessing on killing The Flash, drawing pictures of it and cutting out tree decorations in the shape of the lightning bolts.
Joe walks Barry to the prison, explaining that Mardon will throw Patty off her guard. She's determined to go after Mardon, though, and leaves.
At an old Trickster hideout, Mardon says all three of them want The Flash dead. Cold asks him what makes Mardon think he can do it with the extra backup and The Flash being weakened by Zoom. Snart and Mardon are just about to start fighting each other when Jesse cools them down.
At S.T.A.R., Cisco comes up with the idea to develop the Weather Wand, and Barry tells the whole group that he knows Cisco did that once before -- in the timeline he erased last year. He leaves and waits at his lab with Iris to talk to Joe. She tells him that Francine was pregnant when she left, and Joe walks past her to process. Looking out the window, he asks for more details and Iris tells him that the son is Wally. Joe leaves to go back to work, saying that he needs time.
When Iris and Barry arrive home, Snart is there waiting for them. Barry pins him to the wall and threatens him, but Cold says he's rigged his gun to blow up if he drops it. Snart says he isn't interested in helping kill Barry, but when Barry tries to recruit him to help track the others down, he passes on that, too.
At S.T.A.R., Joe is standing alone, thinking about a time years ago when Iris was sick at school and he had physical symptoms, knowing that Iris needed him. He feels bad that he's never had that for Wally, and that he didn't take any steps to track down Francine after she left; he said he was being selfish, and Wally paid the price. Barry tries to pull him out of the nosedive.
At the police department, Patty and Captain Singh watch the TVs as Trickster takes over the signal and tells the city he wants to kill The Flash, and calls him out. The team figures out where Trickster is broadcasting from by noticing a background detail and tracking him down to a toy company. When The Flash arrives, Patty is already there -- and so is a small (literally) army of deadly dreidels.
Flash grabs Patty and creates a cyclone, lifting them up and out of the toy factory. Outside, she explains her motivations to The Flash -- she blames herself for the stickup that got her dad killed because she ditched work at the family business that day -- and leaves.
At S.T.A.R., Barry calls Patty, who isn't answering. Jay and Caitlin show him the wand prototype.
At the mall, Trickster is impersonating Santa and handing out boxes to kids to open the next day.
In the Breach Room, Zoom pops into S.T.A.R. Labs, and tells Wells he has to "decide," then gives him one more day to do so, and jumps back into the breach.
Team Flash use a device they conjured up to figure out Mardon is about to attack the tree lighting ceremony. When Barry finds him on a nearby rooftop and tries to stop him from attacking the crowd using the wand, Weather Wizard flies away. Barry deactivates Mardon's powers. He comes crashing to the ground in the town square, where Santa-Trickster is. They explain that they've handed out about a hundred bomb-boxes to kids, and Barry has to let them kill him, or they'll set off all the bombs.
At S.T.A.R., Cisco and Wells figure out a way to track down the bombs and set about doing it. Barry is being slowly killed while they track down the first of the bombs.
As Weather Wizard hands The Flash over to The Trickster to finish, the team uses a drone to send that first bomb through a breach in the sky above the city They manage to tweak it to attract the others and pull them all through the breach. Once the bombs are all gone, Cisco calls out to Barry's headset and tells him the bombs are gone, allowing Barry to use his speed and the weather wand to take both villains down in seconds.
Then, however, Patty shows up and, using Cisco's "boot" device from the season premiere, immobilizes The Flash so that she can kill Mardon. Barry manages to talk her down, though, and she arrests Mardon. Jesse is suitably impressed.
At S.T.A.R., Joe comes to see Barry. He's talked with Francine, and tells Barry that he didn't realize he needed to forgive her. He's excited to meet his son.
Joe gives his watch -- a gift from his father -- to Barry, saying he's always said he would give it to his son.
From the computer terminal at S.T.A.R., Barry tells Wells through the two-way mirror that "he" (the other Wells) was right -- that maybe he'll really never be happy...but only if he hangs onto his hatred for Wells. He says he forgives him. Just then, Wells-2 sees him looking at him and calls up on the intercom, asking if Barry needs him for something. Barry invites him over for Christmas, but Wells says he can't celebrate without his daughter.
At the West home, Jay helps Caitlin hang mistletoe, and they kiss. There's a knock at the door, and it's Patty. She says that she needs to tell Barry about something she's been dealing with alone, and brings him a matching Christmas sweater to hers.
There's another knock at the door...it's Wally. Joe invites him in and introduces him to Iris.
Later, Zoom comes to meet Wells, telling him time is up. Wells says he knows why he's sending villains: he wants Barry to get more powerful, and faster, to fatten him up for slaughter. Zoom brings Jesse to him, and then takes her away and tells him to decide. Wells says he will help Zoom steal Barry's speed in return for Jesse's life.