Oliver's heavy-handed approach to getting information from his mother backfires and she manages to shoot him in the shoulder. He turns to Felicity Smoak for help getting back to his hideaway. She and Digg do their best to nurse him back to health. Flashbacks to Oliver's time on the island reveals an early attempt to escape. Oliver's loyalties however prevent him from taking advantage of the situation. The reason for Yao Fei's betrayal is revealed.

After a major fire, Oliver decides it's time to eliminate real estate developer and slumlord John Nicol, another person on his father's list. He's beaten to the punch when another vigilante, The Savior, who kidnaps Nicol and ultimately executes him - broadcasting the whole thing over the Internet. The new vigilante is identified as a man whose wife was killed in a bodega robbery in the Glades district. When he kidnaps Thea's new boyfriend, Roy Harper, Oliver decides to stop him. Meanwhile, Laurel is upset to find that her father has come around to her mother's belief that her sister may still be alive. In a flashback to his days on the island, Oliver learns why Yao Fei refused to leave.

Vertigo is again appearing on the market even though The Count, who created the drug, is still in a psychiatric hospital. Soon after Oliver confirms that he's still there, he somehow manages to escape. The Count's psychiatrist says his patient overpowered him and has concluded that his insanity was just a ruse. The police suspect Tommy may be dealing drugs from the club and Det. Lance gets a search warrant. Oliver is not sure what to believe and Tommy, feeling his onetime friend has no respect for him, quits. He turns to his father for a job. Digg gives information about Deadshot to a former intelligence colleague. On the island meanwhile, Oliver begins to learn how to use a bow.

Oliver decides that his next target is going to be someone on Digg's list: Deadshot. They set a trap for him and Digg's spy friends get involved as well. Meanwhile, Laurel's latest clients are Eric and Nancy Moore who have agreed to testify against Edward Rasmus, a financial advisor who swindled them. The night before their deposition however, they are assassinated. Laurel takes charge of their now orphaned son, Taylor, but he saw his parents killed and is now the assassins next target. Oliver steps in to stop him but in doing so fails to back up Digg and Deadshot escapes. It creates a rift and Diggs walks out. A flashback to the island show Oliver, Wilson and Shado are preparing to free Yao Fei.

The time is fast approaching for the Undertaking to occur and Malcolm Merlyn begins to tidy up the loose ends, beginning with the scientists at UNIDAC. Oliver and Digg trick Moira into telling just what the Undertaking is about. Oliver realizes that even if he manages to eliminate everyone on his father's list he has only, in his own words, eliminated the symptoms and not the disease. Felicity locates the UNIDAC device - sort of. Thea and Roy's relationship comes to head when they are unable to locate the vigilante. Walter files for divorce. Laurel and Oliver begin a new relationship. In a flashback to his time on the island, Oliver learns just what Edward Fyers' plan is.

Oliver awakens to find himself Malcolm Merlyn's prisoner. He manages to escape and away with help from Digg. Malcolm accelerates his timetable as a result. Felicity is questioned by Det. Lance about her hacking activities but is interrupted by Oliver who tells him about Malcolm's plan to destroy the Glades. Tommy confronts Oliver about Laurel but refuses to believe that his father is up to no good. Malcolm comes clean about his plans and Tommy realizes that his father is insane. Moira goes public with what she knows, urging the residents of the Glades to evacuate. Roy and Thea get caught up in the mayhem. While Oliver and Digg go after Malcolm, Felicity tries to neutralize the device via Lance. Malcolm has planned it all very well, however. In a flashback to his time on the island, Fyers attempts to bring down an airliner.

Diggle and Felicity return to the island to convince Oliver to return as the Arrow.

Now that Oliver no longer has the list to work from, he's not sure what's next. Roy continues doing his own vigilantism and has to be bailed out of jail by Thea. When he mentions to Oliver that someone is hijacking medical deliveries to the Glades Memorial hospital, the Arrow knows exactly what he wants to do. His visit to the hospital doesn't go well when local politician Sebastian Blood takes him to task for what his family has done. When he tries to stop a hijacking, Arrow comes up against China White and her new partner Bronze Tiger. Thea tells Roy she's not going to wait around until he gets killed. The flashback to the island shows the aftermath of Oliver's violent attack on the unknown visitor. Shado takes him in hand.

When a dangerous criminal from Lance's past (MICHAEL EKLUND) escapes from prison, Felicity offers herself up as bait so Arrow, Diggle and Lance can capture him...but plans go awry.

Amanda Waller sends A.R.G.U.S. agents to kidnap Diggle. Waller informs Diggle that Lyla has gone missing after following a lead on Deadshot in Moscow. When Diggle tells the team he's headed to Russia to rescue Lyla, Oliver and Felicity decide to join, but things get messy when Isabel shows up on the tarmac and insists on joining Oliver's "work trip". Meanwhile, Moira's lawyer, Jean, tells Thea that dating Roy, a known criminal, is hurting her mother's case.

Oliver is concerned when a mysterious illness sweeps the city, infecting hundreds of people, including Diggle. Oliver discovers Vertigo in Diggle's blood and realizes The Count has broken out of prison and is once again distributing his drug. Meanwhile, Moira goes on trial for her participation in the Undertaking. ADA Adam Donner collapses in court with Vertigo symptoms so Laurel must step in and try the case against Moira. Oliver is torn between standing by his family during the trial and catching The Count. However, things change when Felicity follows a lead and walks straight into a trap set by The Count.

After an impossible break in at Queen Consolidated, CSI Barry Allen comes to Starling to help with the investigation, Sin asks Roy for help so Thea tags along.

After a fight with Cyrus Gold, aka the Acolyte, Oliver is drugged and left for dead. Determined to cure him, Felicity makes a risky decision. The cure causes Oliver to hallucinate, and what he sees forces him to confront his past. Meanwhile, Barry Allen continues to help Felicity, and their connection grows stronger. The Arrow asks Quentin to look into Gold, but when the stakeout on Gold goes bad, someone is killed. Roy is captured and tortured by Brother Blood.

Oliver is shocked when he learns that Slade has come to Starling City. Back on the island, as Oliver, Slade and Sara prepare to take over the freighter from Ivo, Sara pulls Oliver aside and tells him he needs to kill Ivo to prevent him from telling Slade what happened with Shado. Oliver feels immense guilt over the situation but realizes Slade's growing rage from the Mirakuru makes him unpredictable and he could turn on his friends if he thinks Oliver is to blame. Oliver agrees to kill Ivo and the battle begins.

Lyla asks Diggle to go on a mission alongside the Suicide Squad, a team assembled by Amanda Waller to undertake high-risk missions, even though the team includes Diggle's nemesis, Deadshot, and Oliver's enemy, Bronze Tiger.

After taking a ride home from Slade, Thea becomes his prisoner. Can Oliver and his friends save her? Also, someone close to Oliver is working for Slade, since his return from the Island after Tommy's death.

The mirakuru sends Roy into a rage rampage across the city. Sara thinks that the only way to stop him is to kill him but Oliver thinks he can still save him. Meanwhile, Slade is continuing his plan to make Oliver pay.

As Oliver's face off with Slade escalates, his resolve to the no-kill rule is tested. Especially as Slade targets the woman Oliver loves.

Oliver thinks about the offer Ra's Al Ghul gave him, but to do so theres a catch.

During an attack on the mayor's office, Ray is critically injured. Felicity is pleasantly surprised when her mother, Donna Smoak, shows up at the hospital to offer her support. With the SCPD out in full force looking for the assailant, Oliver and his team work hard to stay one step ahead of the police to find the man responsible. However, things come to a head when Ra's al Ghul kidnaps Captain Lance.

The team faces off against a formidable villain nicknamed The Calculator (guest star Tom Amandes). Meanwhile, Nyssa (guest star Katrina Law) makes her move and Roy Harper (guest star Colton Haynes) returns to Star City.

Black Siren returns to give Chase help; Felicity plans a birthday party for Oliver; Lance is angry with Rene for missing the custody hearing about his daughter.

As Slade continues to uncover clues about his son's last few years, Oliver makes a big decision. Meanwhile, the Green Arrow leads the team into battle against "The Dragon," a villain who is stealing valuable tech in Star City.