The Lone Gunman begins with Arrow going after James Holder. The crook sells defective smoke detectors to low-income housing, and by doing so he has indirectly taken lives of people who died in fires.
To get his attention, Arrow shoots Holder's glass of wine, but before he could get any answers from him two shots are fired from another location, hitting James square in the chest, which causes him to fall into the pool he was standing beside. Arrow tried to return fire, but only became the snipers next target. He manages to escape, but not before getting clipped by one of the bullets.
After Oliver returns to his hideout, and begins tending to his wounds, he finds himself getting very dizzy. The sniper's bullet was poisoned! He quickly takes an antidote from his chest, then passes out.
In his dreams, he is back at the island. He is in a cave with Yeo Fai, the man who shot him. He explains that he shot him to protect him, gives him some of the same herb that Oliver took for the antidote, them pulls the arrow out.
After Oliver wakes back up, he realizes that he spent the whole night at his hideout and quickly runs back home. Once there, he finds out that Thea had a wild night involving lots of drinking and breaking into a store. Moria is upset with Thea's behaviour, but still lets her decide to take a sick day from school. Not happy with what just happened, Oliver tells Moria that he was the same way, but wishes he had more parenting so he didn't go through that phase.
Back at Holder's Quentin and Hilton argue over whether Arrow was to blame for the death or not. There are arrows at the scene, but Quentin doesn't think it his style since James was killed by bullets.
Back at his base, Oliver checks the bullets and confirms they are laced with curare, a very rare and powerful poison. By checking through classified records, which he somehow hacked into, he learns that only one killer uses this tactic, Deadshot. With this news, all the other names gets bumped down as he goes to the top of his to do list.
At an unknown location, we get our first glimpses of Deadshot's tattooed body, with Holder's name now branded into his arm, and several other victims complete his artwork.
Afterwards, Oliver takes Tommy, with Diggle following, the factory to reveal his plans to turn it into a club. Oliver's plan is to cover up his base of operations so he has an excuse to be away from home, but he keeps that to himself. His friend points out he has no experience in doing so and recommends checking out another club run by Max Fuller. There is a catch. Oliver and sex with Fuller's wife just before they were married, so he will not be happy to see Oliver again. That doesn't stop them from going though.
After Tommy leaves, Oliver gets Diggle's opinion on the club. He comments it is in a poor part of town, and that the people in the area won't see the money. Oliver states that his hope is to make the area better by having his club there. John thinks that he is just trying to be the area's white knight, and hints that he knows more than he is letting on.
At the law office, Joanna catches Laurel swooning over news about Oliver. Upset that she still hasn't gotten over Queen, Joanna tells her that they are going to a club, if she likes it or not.
At home, Moria changes her tune with Thea and tells her to return home after school as she is grounded. Thea is very upset and comments that she is only punishing her because of Oliver.
Near the events of Holder's death, Oliver uses his amazing climbing skills to scale a wall and dig a bullet out of a wall.
At the station, Quentin gets the tests back from the bullets, and learns that they were fired from a rifle hundreds of yards aways and that they were coated with curare. Detective Quentin is now completely convinced that Arrow didn't kill the man. His partner still doesn't see it so Quentin leaves to find his own evidence.
Oliver checks the bullet himself and learns that it came from the Bratvas, as Russian mob that operates in the area. After leaning the trajectory of the shots, he pays Alexi Leonov a visit, a local member of the Bratvas. After meeting him in the hidden basement of the garage he operates, they introduce each other, and Oliver reveals a Bratvas tattoo on his chest. He then tells them that he wants to know who the killer is and where to find him. They agree, but only after checking his background.
Back at the Deadshot's, he tattoos another name in his chest, Carl Rasmussen, while watching the news report on his death. We are also given a glimpse at several other names already on his chest.
After the latest shooting, the two detectives talk to Moria and Walter about their connection to the two deaths. Walter explains that the men were bidding on the sale of a company against him, and that if he wanted to kill off the bidders he would have to do it faster as there are dozens of them involved in the bidding. The detectives warn them to be careful, but Walter informs them that John Diggle will lead the security.
That night, at the club, Tommy and Oliver ditch John at the door, and soon bump into Laurel, then later Thea. Thea is wasted again, so Oliver tells her to go home and that she is hanging with the wrong people. In a fit of rage, Thea announced that Tommy and Laurel are sleeping together after he disappeared five years ago. Tommy tries to apologize, but Oliver just pushes it away as if it isn't an issue.
As Thea leaves, Fuller notices Oliver and takes him to the back room. Tommy stands up for his friend, then Fuller and his goons start hitting them. It doesn't take long before Laurel arrives and takes out of the guards. After Fuller bans them from his club, Oliver learns that Laurel has been taking a few self-defence lessons. Oliver brings up the topic of her and Tommy's relationship, but Laurel pushes the topic away too.
In another quick island flashback, Oliver awakens in the cave again while his new friend is asleep. He leaves the cave and runs through the forest only to find himself caught in a trap.
After the club, Diggle takes them to Carla, his sister-in-law, who works at the local Big Belly Burger restaurant. Oliver notices that Carla isn't wearing a ring anymore, but John doesn't want to talk about his brother. Tommy brings up Laurel again, but Oliver tells him that it isn't a problem. While Diggle is talking to Carla, who is still upset about the loss of her husband, Oliver gets a call from the Russians. Alexi tells Oliver that he is looking for Floyd Lawton, and provides his last known address.
At Deadshot's, Floyd is checking out blueprints when Arrow arrives. Another heated gun/bow battle ensues, but Deadshot escapes. Oliver grabs his laptop and takes it to Queen Consolidated's IT department where he meats Felicity Smoak. He tries to convince her that the bullet holes are from coffee damage, but she doesn't buy it. She takes the laptop and tells him she will recover what she can.
Back at the mansion, Moria gives Thea dresses for Walter's auction. Thea doesn't understand why she has to go. Moria explains that she envied how Robert could get through to her and that she wants her to be there. Thea points out that this is the first thing that Moria has brought up since Robert's death.
Felicity finds the blueprints on the laptop for the Exchange Building, and that the laptop belongs to Walther Patel. Oliver figures out that he is behind everything so that he has less competition. He is going to need help on this one, so he visits Quentin under the guise of Arrow and gives him what he needs to get his help. He also warns him that everyone will need bulletproof vests as the bullets are poisoned. He then leaves the laptop in his car with the proof he needs.
At the Exchange Building, the auction is about to begin. The police arrive suddenly and arrest Patel, then the detectives check in on their men, but unknown to them, Deadshot already got to one of them.
Tommy meets up the Laurel after work to talk about Oliver's reaction. She tells him that she believes that he knew already and knows that he can't just them. Tommy shows he is still interested in being with her and sets a date with her.
Back at the Exchange Building, Oliver finds Quentin and thanks him for being there to protect his family. When Diggle asks how he knew, he claims he heard it on the radio. Once he notices Thea is there too, he runs over to them to get them to safety just before Quentin notices a bead on Walter's chest. Due to Quentin's quick dive, the bullet misses Walter and kills an innocent waiter instead.
Panic fills the building as more bullets rain down. Oliver tells Diggle to get his family to safety, then runs up the stairs, collecting his disguise on the way. Diggle still follows behind, noticing the odd mess that Oliver has left in his wake. Arrow confronts Deadshot at the tower and the two exchange shots once again. After missing each other several times, Arrow is hiding behind a post, and Deadshot tells him how much he admires his work. Arrow tells him that he isn't the cold killer he is, then firing a quick shot hitting him in the eyepiece. It appears that Deadshot is now just dead.
A noise behind him gets Arrow's attention, and he notices that Diggle has been hit by one the bullets from their fight.
At the island, Oliver's new friend frees Oliver from the trap and tells him it is dangerous for him to be alone. A short while later, several masked men come across what is left of the trap.
Oliver takes Diggle to his hideout to give him the antidote for the poison. As John awakens, he sees Oliver in the Arrow suit.