The episode opens with Barry musing about what he does on his day off -- he's hanging out at S.T.A.R., playing games with Wells, Caitlin and Cisco. Notably, he's playing chess with the too-clever Wells.
An armored truck marked with the Blackhawk Security logo passes by and two motorcycles and a tow truck come up on it, hooking the hoist to the armored truck and stopping it, then knocking out the guards. All the while, they're counting down seconds.
Before they can get away, Barry gets the call and The Flash rushes in to foil their plans. They get away, though, while Barry helps the driver who'd been shot get to the hospital.
Joe and Thawne are called to the scene of the robbery. Barry shows up late, identifying that there were four people involved with the robbery, and that one of the crooks had used liquid nitrogen to crack the hinges on the armored car. Once they're alone, Barry tells Joe that he got a look at one of the guys' faces.
The crooks also didn't get away with anything; they were apparently after the Kahndaq Dynasty diamond, which
Back at the police department, Barry speed-reads through the mug shots and finds Leonard Snart, whose father is also in prison (a dirty cop who used to beat his family). Joe heads off to try and build a case, and Iris shows up. First frustrated that Joe gruffly rebuffs her offer for coffee, she then focuses on Barry, asking him to see the casefile on the armored car robbery, which somebody claims "the Streak" has foiled. He tells her that he can't share an open casefile with her, and they argue all the way to the lab, where they meet Felicity.
Snart and his group, wondering what went wrong, are going over footage from the armored car robbery. Snart had perfectly timed out the robbery, thinking that the distance from police made them safe. One of his men, who had tried to shoot a guard before Snart stopped him, tries to quit and Snart shoots him. He says that the Flash is a man, and that they're going to have to up their game.
Felicity and Barry are walking through the park, she guilts him a bit about not calling. She hints that she knows about his speed, and says she wants to see it. He takes her phone and speeds to the top of a nearby building, snaps a photo of her and runs back, his shoes slightly smoking. When she's disturbed by that, he tells her that he has a frictionless suit for when he's superheroing, and offers to show her where he got it.
He brings Felicity to S.T.A.R., where she reacquaints herself with the team, now that Barry has blabbed that she works with Arrow. They both decline to tell Cisco and Caitlin who Arrow really is. Wells wheels up, greeting Felicity apparently for the first time. He knows her work well; he had speculated she would do great things. Barry offers to show her his speed; he's doing so on the treadmill when she starts asking lots of questions; Wells assures her Barry is in good hands.
Waiting outside the museum where the diamond is going to be, Eddie tries to explain himself to Joe, who says he doesn't want to know about their relationship.
Back at Jitters, Iris tries to talk Barry and Felicity into coming to trivia night to double date with her and Thawne. When Felicity goes to call work and check in, Iris tells Barry that Felicity is great, and that he should be doing more to get her attention because she obviously came all the way to Central City to see him.
Snart is in a warehouse, where a weapons dealer is showing off some major tech. First, he tries to sell Snart on a concentrated flamethrower, but when he says that he needs to slow things down, not heat them up, the man directs him to a gun that freezes things. He says he stole it from S.T.A.R. after the explosion. Snart asks him who else knows he took it, and when he says "just us," Snart says, "Just me, pal," and blasts him with the freeze gun.
Back at Jitters, at Oswald Loomis's trivia night, Felicity is running late. When she does show up, she's wearing a preposterously revealing dress. She's the only one who likes Barry's trivia team name.
At the museum, a guide is walking a tour group, including Snart, through the building. Snart stops at the diamond, and a curator makes a phone call.
At Jitters, their team is doing really well in trivia. Their dates excuse themselves and Iris tells Barry Felicity is perfect: what's he waiting for?
In the S.T.A.R. lockdown where the gun had been stored, Wells rips Cisco a new one for having allowed the gun to get stolen, saying that he knows how he (Wells) feels about weapons: they don't belong at S.T.A.R. He tells hime to figure out a way to find it.
Joe responds to the curator's call; he'd been told to call if there was anything suspicious and that a man -- Snart -- had gone through the tour twice. Joe sees that it's Snart and calls it in, asking for backup. Barry and Thawne are called away from trivia to respond.
When he arrives, Barry finds that Snart has frozen over the road using the gun, causing a police car to spin out and almost hit Joe. He heads into a nearby theater and when The Flash goes to stop him, he starts firing the weapon off at everyone in the building, forcing Flash to dart around saving them all until he misses one and Snart makes his escape while Barry grieves the mistake.
Back at S.T.A.R., Barry is still injured by the shot he took from Snart's gun. It slowed him down -- enough so that he's still healing, and that he missed saving the man who died at the museum. Felicity asks how somebody who never finished high school managed to build a weapon like that, and Cisco admits it was him: he created it to stop Barry if Barry came out of the coma and was a bad guy. Barry starts to get upset, but Caitlin points out that the entire facility they're standing in was built to do good, and it exploded. He asks why they didn't tell him -- and blames Cisco for the man who died.
Back at home, Iris confronts Joe about the silent treatment she's been giving him. He tells her he isn't mad -- that he's upset because he can't be totally focused on the job anymore; that now, he has a part of him seeing his partner as Iris's boyfriend and it puts extra pressure on him. What if something happened to Thawne? What would he say to Iris?
Snart tells his men that they're going to hit the museum again tonight. When they object, he tells them that his gun can stop both the police and the streak. His men both quit, holding a gun to his head so he can't kill them for doing so.
At S.T.A.R., Felicity goes to see Barry, who's running himself ragged on the treadmill. He can't sleep, having flashbacks to watching him die. He says he has to go faster. Felicity tells him it isn't his fault, or Cisco's. Barry says he understands that Cisco didn't trust him. She tells him that Team Arrow had similar trouble at first and that the path is lonely -- that he shouldn't make it any lonelier than it has to be.
At the museum, Snart blasts through the door with the cold gun and walks up to the diamond.
At S.T.A.R., Cisco has figured out how to ping the cold gun. He needs a half hour to hack a satellite, but Felicity can do it in under a minute. She figures out where Snart is -- near the train station -- and they figure out he's probably already got the diamond. Joe, Thawne and Barry converge, but Snart takes out the bottom of the moving train in order to force Barry to save bystanders rather than chasing him, saying he's seen Barry's weakness. Barry gets everyone clear of the train and collapses outside it, where he's blasted with the cold gun.
As "Captain Cold," as Cisco named him, is about to finish him off, Cisco shows up with a much bigger prototype cold gun. He scares Snart off just enough to turn him away, not enough to get him to drop the gun or diamond, before revealing it was actually just the S.T.A.R. vacuum cleaner with LED lights.
Back at S.T.A.R., Felicity praises their team, and says she has to get back to hers. Barry hugs her goodbye, and when Wells praises her, saying she's special, Barry agrees. After everyone leaves, Wells tells Cisco not to ever do anything like that again.
At the police station, Iris comes to see Joe, apologizing again and telling Joe there is nothing he could ever do that would change the way she looks at him. Joe tells her that Eddie saved his life chasing down Snart. Iris agrees, "From now on, no more secrets." She leaves to go see Eddie.
Barry comes to see Felicity on the train; she's figured out that it was Iris he crushes on who doesn't reciprocate. He tells her it's like her and Oliver. He admits that he's afraid it will change everything if he tells Iris. She says it will, but maybe that's not such a bad thing. They agree that they're perfect for each other, but that they're sitting there pining for people they can't have. They agree that if the other ever needs them, they'll run as fast as they can, and kiss, then Barry speeds off.
Snart goes to see Mick, an old partner of his and a pyromaniac, with the flamethrower he'd rejected, saying that to function in Central City they needed a new kind of team.