A notorious criminal named Leonard Snart obsessively pursues the theft of a famous diamond with the help of an Absolute Zero gun stolen from Star Labs. The gun is designed to stop the Flash, so apprehending Snart is more difficult that it seems. Meanwhile, Felicity Smoak (from Arrow) visits from Star City to spend some time with Barry.
Leonard Snart and his team perform an elaborate heist on the armored truck transporting the famous Kahndaq diamond to the Central City Museum for exhibition. Snart knows all the emergency response times and has timed his robbery to be in and out before anyone can arrive. However, Barry is there in seconds and foils the robbery. One of the guards gets shot, and instead of chasing down Snart and his gang as they cruise away, Barry takes the guard to the hospital.
Barry identifies Snart from his mug shot and Joe tells him that once Snart has his eye on something, he won’t stop until he has it. Snart obtains a weapon from Star Labs, designed by Cisco to stop the Flash, and makes an attempt on the museum. While Snart doesn’t get the diamond, a man is killed by the high-tech freeze gun as Snart distracted Barry by shooting at random bystanders.
Back at Star Labs, Wells tells Barry that the gun is theirs, that Cicso designed it before Barry woke up from his coma in case he turned out to be unstable or evil. Barry is furious that he wasn’t told earlier so he could have known what he was up against and prepared for it. He understands why Cisco designed the gun, but feels betrayed that it was kept a secret after the fact.
Snart makes a third, successful attempt on the museum and escapes on a train with the diamond. Barry catches up with the train, where Snart tells him he knows his weakness. He can’t chase him down if he’s busy saving everyone else. Snart uses the gun to crash the train, jumping off before the chain reaction begins. Barry saves everyone from the train before the crash and still has time to confront Snart, who shoots him with the gun. Barry is disabled, but Cisco, Caitlin, and Felicity show up with the prototype for the cold gun and threaten to shoot Snart if he doesn’t leave Barry alone. Snart agrees, but still makes off with the diamond. The “prototype cold gun” turns out to actually be the Star Labs vacuum cleaner decked out with a lot of LED lights.
Elsewhere, Snart makes a proposition to a shadowy figure named Mick who plays with matches that they team up to do some crime. Snart offers him a heat weapon, another among the weapons offered to him by the Star Labs janitor who stole the cold gun. The shadowy figure agrees and examines the heat weapon fondly. It seems pretty likely that this shadowy figure is Mick Rory, otherwise known as the villain Heat Wave and that their collaboration is the start of the Rogues.
The Rogues are a loose association of criminals with a general code of conduct. Captain Cold and Heat Wave are two of the eventually vast number of meta-humans and criminals that come to be known as Rogues. This association and its members are mainly adversaries of the Flash and rather than anything really nefarious, mostly want to carry out heists and robberies. They even have a rule about no killing unless absolutely necessary, and absolutely no killing women and children. Captain Cold is their founder and leader, so his proposition to Mick Rory certainly foreshadows the start of this organization.
Felicity and Barry met during an episode of Arrow, where the two fast became close friends. Felicity shows up randomly to see Barry after overhearing the conversation he had with Oliver Queen, knowing both that Barry’s awake from his coma and that he’s the Flash. While they’re clearly fond of each other, and in Felicity’s words “perfectly perfect” for each other, they both pine away for people they can’t have. Everyone Barry knows encourages him to pursue Felicity, telling him that they’re perfect for each other. As Felicity travels back to Star City by train, Barry catches up with it to talk with her one last time. They both acknowledge that their hearts belong to another, hopeless as it may be, but pledge their support and friendship to each other. Barry kisses Felicity goodbye.
When it is revealed that Cisco designed a weapon capable of killing Barry, Wells is furious with him. Not only is he against weapons at Star Labs, but it is a weapon that puts Barry Allen at risk. Considering that Wells is mysteriously and obsessively protective of Barry and the legend who will become known as the Flash, this weapon complicates everything Wells is trying to accomplish.
On the other hand, Barry is also furious with Cisco, not so much for designing the weapon in the first place, but for not trusting him with the knowledge of its existence once Barry came to be trusted by the group. Barry feels betrayed, that all the trust he puts in Cisco isn’t reciprocated. What’s worse, a man died because Barry wasn’t prepared to challenge the weapon. In the end, they all come to an understanding – all except for Wells, who in no uncertain terms tells Cisco never to do something like that again.
Iris and Joe
Joe is still having some issues accepting that Iris and Eddie are dating. He gives Iris the cold shoulder and tells Eddie that they’re not friends, they’re partners. Iris finally confronts Joe. Iris thinks that Joe is mad at her for dating his partner, when that’s not actually what’s going on. It’s difficult enough that Joe is responsible for Eddie as his partner, but now that he’s his daughter’s boyfriend, that makes the daily danger they face together ever more difficult. He’s afraid that if anything were to happen to Eddie that Iris might look at him differently, and might never forgive him. He says simply that her relationship with Eddie makes things complicated. Iris promises that nothing Joe could ever do would change how she looks at him. They come to an understanding and Iris says “no more secrets,” to which Joe half-heartedly agrees. He is still, of course, keeping Barry’s secret, even as Iris becomes more and more fascinated by the Flash – even starting a blog about him.