In the wake of mass destruction in the Glades, Oliver is convinced to return home to find his family in disarray and his city under new threats: vigilantes who are out for blood, who have set their sights on the Queen family.
Oliver faces off against China White and her dangerous new partner when they begin stealing medical supplies bound for the Glades' hospital. Meanwhile Oliver looks for a way to help the Glades publicly, and Thea gives Roy an ultimatum.
A serial murderer who Officer Lance put away years ago escapes from prison, and Oliver agrees to help Lance catch him again. Thea visits her mother in prison, and Roy is tasked with finding a mysterious new player who has arrived in Starling City.
Oliver has a decision to make after discovering the true identity of the new girl in town. Meanwhile, the team targets a new crime lord who is bringing military-grade weapons into the Glades.
After Oliver introduces Sara to his team, she is targeted by a highly-skilled member of the League of Assassins. Meanwhile, Moira considers a plea deal that could spare her the death penalty.
When Diggle receives new information about his missing friend -- and the man who shot his brother -- Oliver and Felicity join him on a trip to Moscow, where he infiltrates a Russian prison to save Lyla.
Moira's case comes to trial, forcing her to reveal a very personal secret. But Oliver is distracted by the escape of the Count, who uses an altered form of his Vertigo drug to attack the city.
Central City police scientist Barry Allen arrives in town after a super-strong thief steals a piece of scientific equipment. Sin asks Roy for help in finding a missing friend, and in the past Oliver and his friends search for a way to cure Slade.
After a close encounter with death Oliver has hallucinations of Shado and Slade, forcing him to confront a fateful encounter with Ivo on the island. Sebastian Blood plans to mass-produce his serum, and the police find Cyrus Gold to be more than they can handle.
When a rogue bomber terrorizes the city, Sebastian Blood calls a rally to stand against him. Laurel investigates Blood, and on the island Oliver watches as Slade's mind is affected by the serum.
Laurel approaches the Arrow with information on Sebastian Blood, pointing to his possible connection to the man in the skull mask. Roy confides in Sin about his super-powered secret, but gets in over his head.
While Arrow attempts to train a rage-filled Roy, the criminal known as Bronze Tiger is sprung from prison to help steal a dangerous technology. Laurel spirals out of control after losing her job.
Sara returns to Starling and is confronted by the daughter of Ra's al Ghul, who targets the Lance family to force Sara back to the League of Assassins.
The team faces off with a brilliant thief who has acquired a key to open any bank vault, and Felicity puts herself in danger in a desire to prove her worth. Oliver throws a homecoming party for Sara, and on the island Oliver, Slade, and Sara encounter a pilot shot down by Ivo's freighter.
On the island, Oliver, Slade, and Sara plan to infiltrate Ivo's freighter and escape the island for good. In the present day, Oliver searches for a way to keep his family safe when Slade turns up in their home.
Diggle is recruited by Amanda Waller to steal a deadly weapon from a warlord he knew from his time in Afghanistan. Oliver is put on edge by Slade's threats against his loved-ones, and tries to put distance between himself and Sara.
The arrest of Frank Bertinelli draws his daughter Helena back to Starling City, and puts Laurel in the crossfire when she is assigned to prosecute his case. When Huntress seizes the courthouse, the Canary will stop at nothing to save her sister.
The Queen family is thrown into disarray by the abduction of Thea, but Arrow doesn't get the outcome he wants after handing Slade over to the police. Isabel makes a move against Oliver, and on the island Sara hatches a plan to ambush Slade.
After Oliver and his team cripple the serum's production Slade makes a direct assault on their home, planning to steal what he needs to continue his plan. Oliver must convince an angry Thea to help save the family fortune, and Laurel considers the information given to her by Slade.
The team pursues Roy across the city after he awakens in a blind rage caused by the Mirakuru. Moira makes a decision after another conflict with Thea, and remembers a confession from her son seven years ago.
Oliver goes missing after all but giving up in the fight against Slade. But when Laurel reveals Blood's connection to the enemy, the team must race to stop an army of Mirakuru soldiers from laying waste to the city.
Starling City is under seige as the police find themselves ill-equipped to repel an invasion of Mirakuru soldiers. Oliver, Felicity, and Diggle race to secure a cure from S.T.A.R. Labs, and Malcolm Merlyn returns for his daughter. On the island Oliver goes in search of Sara, knowing it may be a mission he will not survive.
New hope for stopping Slade's army emerges in the form of new allies and a viable cure for the Mirakuru, leading Oliver to a final showdown. Meanwhile Laurel is kidnapped, and Diggle and Lyla infiltrate A.R.G.U.S. after they target the city for destruction.
