Season 4 of the CW network's “Arrow” continued its wild ride trajectory in episode 3 with the introduction of yet another DC Comics villain. As Oliver (Stephen Amell) and Diggle (David Ramsey) struggle to patch up their relationship, the villain Double Down starts wreaking havoc on Star City. 

The episode opens with Diggle and Ollie struggling to take down two of the “Ghosts” working for Damien Darhk (Neal McDonough). They find themselves with a distinct lack of boots on the ground as the two thugs use some unexplainable mystic powers to get away. The duo returns to the lair and it becomes clear that neither are going to be seeking forgiveness from the other for the way they’ve been acting. This means the only two team members left in town can’t stand each other. After all, Thea (Willa Holland) and Laurel (Katie Cassidy) have gone to visit Malcolm Merlyn (John Barrowman) and Nyssa (Katrina Law), who are each making their return to Season 4 in the episode. 

Laurel makes good on her promise from last week to use the Lazarus Pit that brought Thea back from the brink of death to bring back her sister, Sara (Caity Lotz), who has been gone for almost two years. Naturally, Malcolm, who didn’t want to use the Pit on his daughter, Thea, in the first place, says no. In a rare moment, Nyssa agrees with him, but Laurel is both silly and determined to make it happen. 

Meanwhile, Diggle goes back to his house to find that his wife and baby are gone. Inside is an A.R.G.U.S. agent. He tells Diggle that, despite breaking into his home, he means him no harm and that his family just happens to be out for the night. He brings Diggle information about the man that hired Deadshot (Michael Rowe) in 2009 to kill his brother. Her name is Mina Fayad (Carmen Moore), and she’s just arrived in Star City with a new friend. She shows up to a meeting with Darhk to inform him that she was sent by his mysterious benefactors, H.I.V.E., to help with his growing vigilante problem. It turns out, her associate is the DC Comics villain Double Down, who uses dark matter-infused playing card tattoos to throw a lethal deck at his enemies. Darhk tells him that he’ll pay him big money to take out the Green Arrow, but when he lures Oliver into a trap, the hero manages to fight his way out of it. Unfortunately, he takes a playing card to the arm in the fray. Meanwhile, Diggle almost gets shot to pieces while following Fayad around town in hopes of finding out why she ordered a hit on his brother.

Felicity (Emily Bett Rickards), has finally had it with her two bickering teammates and lectures them both on letting their pride almost get them killed. She says that unless they agree to start working together, she doesn’t want to hear that they’ve left the Arrow cave. Diggle finally reveals his brother’s H.I.V.E. connection to Oliver, and the buddies' relationship is on the mend. Meanwhile, Felicity goes upstairs to find her friend from last week, Curtis Holt (Echo Kellum), who is designing cool gadgets for Palmer Technologies. She asks him to analyze the playing card she removed from Oliver’s arm. 

Back in Nanda Parbat, Thea approaches her father to ask about the side effects she’s feeling from the Lazarus Pit. Malcolm confirms her, and the audience’s, worst fear. He tells her that the only way her bloodlust would go away is if she either killed the person who wronged her, which would be difficult since that person is dead, or simply gave in and satiated her desire to kill once in awhile. Naturally, Thea refuses because she has a policy against murder, so her father takes things into his own hands. While Thea is asleep, two assassins try to cut her throat. She wakes up and both the training and blood lust takes over as she kills them without a second thought. When the adrenaline dies down, it becomes clear that Malcolm sent two of his own men to relieve Thea’s urge to kill. She freaks out with anger and is about ready to leave for Star City, never to see her father again, when he makes a desperate play. In order to get Thea to forgive him, Malcolm agrees to put Sara in the Lazarus Pit. She comes back to life, but she’s hardly the same Sara fans know and love. 

Meanwhile, Felicity and Holt find themselves in trouble as it turns out Double Down is able to track down the location of all his cards, since they’re a part of his meta-human biology. He arrives at Palmer Technologies and attacks the two science buddies. Felicity has no choice but to retreat to the Arrow Lair under the building, revealing her secret to her co-worker. They manage to fight off Double Down, but not without Felicity figuring out a way to track him first. Now that Felicity has been put in danger, Oliver and Diggle mend their friendship a bit more for one final confrontation with the villain. They stop his car as he’s trying to flee both Star City and Darhk and tie him up for interrogation. Being a crafty villain, Double Down gets a hand free and sends a card flying at Diggle’s chest, which Oliver dives in front of. Diggle beats Double Down within an inch of his life and checks on Oliver, who is OK thanks to his armor. Still, his partner is taken aback by the fact that he’d take a metaphorical bullet for him. Just like that, their relationship is officially mended. 

Despite the big moral win for the good guys, the episode ends in a dark place back in Nanda Parbat. With Sara still not able to communicate like anything but a vengeful animal, Nyssa finally lets her hatred of Malcolm take over. She reveals that her father developed a way to destroy the Lazarus Pit, which she’s used to freeze it over. Just like that, Malcolm finds himself the first man to lead the League of Assassins without the healing power of the pit. The episode ends with a very scared Malcolm ordering Nyssa to be taken away, presumably to her death.