Oliver and Felicity's blissful getaway is cut short when Thea and Laurel pay them a visit and tell Oliver they need his help back in Star City. The city has been attacked by "Ghosts", assassins led by a dangerous man named Damien Darhk. However, when Oliver returns, Diggle makes it very clear that he doesn't want Oliver on the team.
When an old family friend, Jessica Danforth, tells Oliver and Thea that she is going to run for mayor, both Queens are concerned considering the last three mayors have been cuddled. Despite their protests, Jessica makes her announcement so the Green Arrow and Speedy vow to protect her. Meanwhile, Thea begins to exhibit effects from the Lazarus Pit. In addition, Felicity is faced with a tough business decision and looks to one of her employees, Curtis Holt, for help.
The growing tension between Oliver and Diggle puts both their lives at risk when they go after Damien Darhk and a H.I.V.E. deployed meta-human. Meanwhile, Laurel talks Thea into returning to Nanda Parbat to ask her father to put Sara into the Lazarus Pit. However, Laurel is surprised when Nyssa refuses to do it.
Laurel must deal with the repercussions of taking Sara to Nanda Parbat. Meanwhile, Oliver asks Captain Lance for a favor and while he's not surprised at the response, he is surprised at what he finds out next.
When things take a turn for the worse with Sara, Oliver calls in a favor from an old friend who deals in the mystical, John Constantine.
Felicity is frantic when she learns that Ray is alive and being held by Damien Darhk. Felicity's guilt over not finding Ray sooner causes tension between her and Oliver. Meanwhile, Sara joins Laurel, Thea, and the team on a rescue mission for Ray. However, the effects of the Lazarus Pit take over and threaten to jeopardize the entire operation. Donna Smoak returns to Star City.
Team Green Arrow's ongoing battle with Damien Darhk is complicated by a shocking revelation. Thea's bloodlust returns and she loses control in front of Alex.
Oliver and Barry Allen take Kendra Saunders and Carter Hall to a remote location to keep them hidden from Vandal Savage while they figure out how to defeat him. Malcolm arranges a meeting between Vandal, Green Arrow and The Flash that doesn't go as planned. Meanwhile, Felicity, Thea, Diggle and Laurel work with Team Flash to come up with a weapon powerful enough to destroy Vandal Savage.
After the city is attacked again, Oliver makes a bold move against HIVE. Malcolm checks in on Thea and leaves her with a warning. Things take a horrible turn when Damien Darhk retaliates in a brutal manner at Oliver's mayoral holiday party.
While Green Arrow goes looking for revenge against the man who struck at someone close to him, the team deals with the return of Anarky. Meanwhile, Diggle tries to deal with his brother Andy.
Diggle must learn to trust his brother Andy when an enemy of their wartime past, an agent of the criminal organization Shadowspire, pays a visit to Star City. However, Diggle learns more than he bargained for about their shared time at war. Meanwhile, Oliver has to learn a whole new way of life.
While Nyssa usurps control of the League of Assassins from its new leader, Malcolm is busy in Star City tending to his ailing daughter. Meanwhile, the team battles a new villain calling himself the Calculator, and Roy Harper returns to town.
Oliver receives an offer from Nyssa that is hard to refuse. Meanwhile, Thea continues to battle the blood lust, Malcolm steps in to help his daughter, and Laurel has a heart to heart talk with Nyssa.
Oliver and team uncover HIVE's plan to take out Team Arrow once and for all. With HIVE's next attack imminent, Lance wonders if Donna is safer without him in her life. Meanwhile, with the wedding fast approaching, Oliver begins to feel guilty that he hasn't told Felicity about his son.
Oliver realizes he needs help battling Darhk so he calls in an old friend - Vixen. Using her magical ability to summon animal powers, Vixen gets a lock on Darhk's location and the team goes to war. Meanwhile, Thea has a heart-to-heart talk with Malcolm.
A heartbroken Cupid returns to Star City with one goal - to destroy anyone in love. The team learns she's killing couples on their wedding day so Oliver and Felicity decide to pose as bait.
Brie Larvan breaks out of jail and turns up at Palmer Tech threatening to hug everyone unless she gets the bio-chip that is implanted in Felicity's spine. When Oliver realizes that Felicity, Thea and Donna are trapped in Palmer Tech with everyone else, he looks to a surprising ally to help Team Arrow save the day.
The team threatens to break apart when Laurel receives a job offer, Thea is consumed with anger toward her father Malcolm, and Diggle and Oliver disagree on trusting Andy. However, tragedy soon brings them together... and takes one of their own.
Oliver and the team struggle to come to terms with Laurel's death, especially Diggle who is overwhelmed with guilt for choosing to believe Andy had changed. Meanwhile, Lance refuses to believe his daughter is really gone and asks Nyssa to help bring her back. A recent Black Canary sighting in Star City only seems to prove his theory that Laurel isn't actually dead.
While Diggle goes off after his brother, Thea takes a weekend off with Alex but begins to have he doubts that it was a good idea. Meanwhile, Oliver and Felicity travel to Hub City to find a shaman that can teach Oliver how to resist Damien's dark magic.
When Team Arrow learns what Damien Darhk's next move is, Felicity realizes she needs to ask her father, Noah Kuttler, for help. Noah and Oliver have a heart to heart talk that leaves Oliver rattled.
Following the shocking events in the previous episode, Oliver and Diggle race to rescue Thea, while Felicity, Curtis, and Noah join together to stop Darhk,.
Felicity and Curtis try to stop the nuclear countdown, while Green Arrow attacks Damien in an attempt to stop him before he destroys first Star City... and then the world.