- For the titular character, see Barry Allen (Earth-1).
- "The five years I was away, I encountered things that defy explanation."
- —Oliver Queen
|A seemingly impossible robbery at Queen Consolidated's Applied Sciences Division brings Central City police scientist Barry Allen to town. Citing a similar case back home, Barry offers to help Oliver and his team with the investigation. Oliver senses there is more to Barry than meets the eye, but he's distracted by the similarities between this current case and something that happened on the island. Meanwhile, Felicity takes a liking to Barry, which doesn't go unnoticed by Oliver. Sin asks Roy for help when a friend of hers goes missing. Roy is surprised when Thea not only encourages him to help, but joins the search. Unfortunately, Sin's friend is connected to Brother Blood, and their search ultimately gets one of them seriously injured.|
When a masked thief with superhuman strength steals a centrifuge from Queen Consolidated's Applied Sciences Division, Oliver and his team investigate, with the help of Central City CSI Barry Allen, who is a fan of the Vigilante and has many observations and theories about him. He reveals all of this to Felicity, telling her he's interested because his mother was murdered and a person like The Arrow may have been able to stop it.
Oliver suspects that Barry is hiding something and has him investigated by Diggle. When confronted with the fact that there is no similar case in Central City and he's only an assistant CSI, Barry reveals that he is searching for super-powered beings in the hope that he will prove one case true and subsequently, find answers to clear his father for the his mother's murder. He explains the night his mother died, when a blur-like figure entered his home and his father went to fight it. Barry went to help but somehow found himself twenty blocks away. It's implied that the strangeness of his testimony and the fact that he was so far away led the police to believe he was covering for his father, who was arrested and convicted of his mother's murder.
After a blood bank is robbed and Oliver fails to stop the thief, he recognizes the combination of blood and serum and realizes that the thief was enhanced using the same serum that Dr. Ivo was searching for on the island. He reveals this information to Diggle (who had previously suspected he knew more than he was telling) and Felicity adding that he destroyed the entire supply of the serum and all survivors were subsequently killed. He relays to Diggle and Felicity that the serum needs a strong sedative as well, which leads Felicity (aided by Barry) to find the next place the robber will hit. Felicity warns Oliver that that he may not be able to fight the thief due to his strength and muscle density.
Roy and Thea stumble upon Oliver's case after helping Sin to find her missing friend. He was a test subject of Alderman Blood's that didn't survive after being lured in by a blood drive. He contacts Oliver to ask him to investigate, but Oliver brushes him off, telling Roy to stay away, as he is already on the case albeit from a different angle. Frustrated, Roy says he and his friends will investigate themselves, so Oliver shoots Roy in the leg to prevent him (and possibly Thea) from getting further involved.
Oliver tracks the thief to an A.R.G.U.S bunker,where the robber reveals that he is only a follower of "his brother" who "saved" him with the serum. Oliver fights him, losing, and is badly injured. He loses consciousness, having been injected with an unknown substance. Felicity and Diggle arrive and find Oliver weak. Unable to identify what entered his body, Diggle tries to call 911, but Felicity stops him to protect the Arrow's identity. She says she know someone else who can help.
At the train station, Barry has missed his train to Central City and will have to wait until the morning. Realizing he's going to be in trouble, but conceding that it's out of his control, he sits on a bench to wait. From the shadows a dart is shot into Barry's neck and he falls over unconscious. Groggily, he wakes up in the Arrow's hideout, confused by what he is seeing and where is at. Upon seeing Oliver unconscious on a table in front of him, Barry is startled and then is approached by Felicity who begs him to save her friend's life.
Meanwhile, Moira returns to the public eye and is not welcomed in society or by Isabel Rochev at Queen Consolidated. Not only that, but Malcolm has begun to put pressure on Moira to tell Thea that he is her father. Moira tells Malcolm she refuses to be afraid of him anymore. Instead, she has contacted Ra's al Ghul, who wants to kill Malcolm for breaking the League of Assassins' code of honor by destroying the Glades. Moira tells Malcolm to run and as a result, Malcolm leaves and warns her that the issue regarding Thea is not over.
In a flashback to the island, Oliver, Sara, Slade, and Shado travel the island using the amulet to find the sub in a fissure on the island, and find the serum. They have the serum but no sedative, but since Slade will die without it they inject him anyway. Just before they do, Slade apologizes to Shado for not revealing he had feelings for her. When they inject Slade with it his heart stops, just as Dr. Ivo arrives at the sub with his men.
- This episode introduces the character of Barry Allen, who in the comics (and later in the spin-off series ) is the civilian identity of the Flash.
- Barry tells Felicity that he's interested in The Arrow because when his mother was murdered, they never caught the guy and a person like The Arrow might be able to help catch the murderer. This statement actually turns out to be true as Oliver Queen was the one who was finally able to catch Reverse-Flash by using Nanites, after a battle in episode 22 of season 1 of The Flash, "Rogue Air".
- When Oliver tells Diggle and Felicity that he's encountered Mirakuru-enhanced individuals before, he describes the Mirakuru as a serum designed to create human weapons. John then says, "Human weapons? My God, what's next; aliens?" Approximately three years later, Team Arrow (alongside Supergirl, Team Flash, and the Legends) ends up dealing with aliens during .
- Furthermore, this episode introduced Barry. When Barry went to ask Team Arrow to help him battle the aliens three years later, John said, "I swear to God, Barry; my life was somewhat normal before I met you"; a possible nod to the fact that John and the rest of Team Arrow first encountered strange things like Mirakuru soldiers around the same time that they first met Barry.
- This episode is notable as being the first episode of to hint at super-human abilities; previously, the show was considered to be extremely grounded.
- In one shot, the name "Kord" was seen on lab equipment in the Applied Sciences building. This is likely a reference to Kord Industries and Ted Kord.
- In the extended promo of this episode, there is a scene of Barry arriving at Queen Consolidated, which is not featured in the episode.
Preparation ran from September 19 until September 27, 2013. Shooting ran from September 30 until October 9, 2013.
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