The plan to kill Malcolm Merlyn goes into operation. Arrow kills one assassin who has just arrived in the city and retrieves his cellphone. It's up to Felicity to break into it and find out just who the target is. A birthday dinner for Tommy Merlyn is interrupted by his father who brings him a present. Tommy makes it clear that he is not welcome and does not want a relationship with him. Malcolm is to receive an award at a civic gala and after a heart to heart with Oliver, Tommy decides to attend. When Oliver learns that Malcolm is the target, he races to save Tommy. Once the attack begins, Malcolm and Tommy takes refuge in his office and Malcolm is about to reveal that he is the Dark Arrow but is seriously wounded before he can do so. Arrow arrives on the scene and to convince Tommy that he is there to help, reveals his identity.

Helena is back to seek vengeance, but Oliver still has feeling toward her. The Arrow must stop and kill her, but at what costs? Now that several of his closest friends know about his true identity, no one is safe.

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.

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.

The League of Assassins give Oliver 48 hours to find Sara's killer, or Starling City citizens will die. Oliver then has an epic confrontation with Ra's al Ghul.

Oliver and the team struggle to come to terms with a friend's death, especially Diggle, who is overwhelmed with guilt for choosing to believe Andy had changed.