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.

Oliver discovers a man who goes by the name "The Mayor" is bringing illegal guns in to The Glades, so Oliver sponsors a "Cash for Guns" event to help clean up the city. Unfortunately, The Mayor crashes the event with his gang and seriously injures Sin. The Canary is furious when she learns her friend is in the hospital and sets out for revenge. Meanwhile, Felicity stuns Oliver with a bit of information about the Canary, Donner asks Laurel to dinner, and Diggle reconnects with an old friend.

While Oliver tends to the Canary's wounds, he tries to get her to talk about where she came from but she refuses. However, after Oliver and Canary are attacked at the Queen mansion by a trained killer from the League of Assassins, she confesses to how she's connected with the nefarious group. Meanwhile with Moira facing multiple counts of murder and conspiracy for her part in the destruction of The Glades, the Assistant District Attorney offers her a choice - plead guilty now and avoid the death penalty or take your chances in court. Thea begs her mother to fight for her life but Moira seems resolute about taking the offer. Meanwhile, Oliver is furious with Laurel for joining the prosecution's team on his mother's case.

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 must tackle a new threat to the city when bombs start to go off in Starling City. Felicity discovers the person setting them off is Mark Scheffer, a man who goes by the nickname Shrapnel. The Arrow discovers Shrapnel's next target is Sebastian Blood's "Unity Rally" and tries to talk the alderman out of hosting it, but he refuses. The Arrow sets off to stop the bombing, but Shrapnel tricks him and traps him in a bomb-laced antique store where he is unable to move without setting off the device. While Felicity helps Oliver, Diggle races to the plaza to find the bomb before it goes off. Meanwhile, Roy continues to hide his new strength from Thea but, after she witnesses his super strength in action at the rally, she demands answers. Laurel's suspicions about Sebastian grow stronger once she learns that he grew up with Cyrus Gold, the man who killed Lance's partner. After Donner refuses to help her investigate, she turns to The Arrow for help.

When Laurel asks the Arrow to investigate Sebastian Blood, Oliver is unsure whether to believe her accusations. But when they get too close to the truth, Blood strikes back.

Arrow offers to train Roy so he can learn to control his newfound super-strength. However, Roy is a rebellious student and refuses to listen unless Arrow reveals his true identity, which Oliver refuses to do. Meanwhile, the Bronze Tiger escapes from prison and steals Malcolm's earthquake machine to sell to the highest bidder. Oliver, Diggle and Felicity attempt to stop the transfer, but Roy gets in the way, putting everyone in danger. Laurel is disbarred and spirals out of control. Moira is thrilled when Walter asks her to dinner, but his reason surprises her. Thea encourages her mother to ask Walter to reconcile.

Laurel continues to unravel, Oliver and Lance try to convince Sara to stay in Starling City and finally reunite with Laurel and Dinah. However, Sara's fellow League of Assassins member, Nyssa, comes to bring Sara back to the fold, but when Sara refuses, Nyssa kidnaps Dinah. Realizing she's putting her family in danger by staying in town, Sara considers re-joining the league.

Oliver brings Sara into the Arrow team. Watching Oliver and Diggle spar with Sara and talk old scars, Felicity starts to feel left out. The team is investigating a villain named William Tockman, a.k.a. The Clock King, who is a brilliant thief armed with technology that can open any bank vault in Starling City. After The Clock King infiltrates the computer systems in the lair, Felicity feels pressure to prove her worth. When she gets a lead on Tockman's whereabouts, she heads out without the team, putting her in peril. Meanwhile, Oliver throws Sara a welcome home party, but Laurel refuses to attend. After Lance makes his case for a family dinner, Laurel acquiesces, but when Oliver shows up with Sara, she loses her temper on both of them.

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.

When Frank Bertinelli is arrested, Oliver knows it's only a matter of time before his daughter, Helena, AKA The Huntress, returns to town. To make matters worse, Laurel is picked to try Frank's case, putting her right in the path of Helena. Oliver tells Sara he will handle his ex-girlfriend, but when Helena takes hostages at the courthouse, including Laurel, the Canary will stop at nothing to save her sister. When The Huntress and Canary meet, an epic battle begins. Meanwhile, Roy realizes he needs to keep Thea safe, but doesn't like the way he is forced to go about it.

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.

Oliver, Canary, Diggle, and Felicity return to the lair and find Slade waiting for them. An epic battle breaks out and one member of Team Arrow is sent to the hospital. Thea hits her breaking point, but just as Oliver is about to reach her, Slade intervenes and Oliver is faced with a choice - his battle with Slade or his family. Meanwhile, Laurel struggles with a new secret.

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.

After Slade threatens to take everything Oliver loves away, Oliver decides the fastest way to stop further bloodshed is to surrender to his enemy. Knowing that surrender will surely lead to Oliver's death, Diggle and Felicity go to extreme measures to keep Oliver from confronting Slade. Meanwhile, Thea considers leaving town, and Laurel resumes her crusade against Sebastian Blood. Finally, Slade unleashes his assault on Starling City.

Oliver rallies his team as Slade's soldiers attack the city. Felicity gets a call from S.T.A.R. Labs with game-changing news and Thea comes face-to-face with her father.

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.