The penultimate episode of “Arrow” Season 4 brought things to an apocalyptic level as the team battled for control of nukes that could wipe out the world. In the final setup before the big finale on the CW, the hero fought his most dangerous battle yet in episode 22, titled “Lost in the Flood.” 

The episode opens right where last week’s left off, with Oliver (Stephen Amell) and Diggle (David Ramsey) confronting the villain Damien Darhk (Neal McDonough). After letting one of the nuclear weapons hit a city, the baddie has more than enough juice to be unstoppable. Drunk off his own confidence, he allows the duo to live so that they can experience the apocalypse and watch their loved ones die.

From there, they retreat back to the lair where Felicity (Emily Bett Rickards) informs them that the missing Thea (Willa Holland) finally got in touch with them. She says she’s being held captive by her father, Malcolm Merlyn (John Barrowman), but wasn’t able to reveal that she’s in Darhk’s new world order bunker underground. Just after she sends the message, Merlyn enters and drugs her with the same compliance method that’s kept everyone living so happily underground while the world supposedly ends above them. 

While this is happening, Darhk is solidifying his plan by having his wife Ruve Adams (Janet Kidder) and Merlyn deal with the intruder, Lonnie Machin (Alexander Calvert). Additionally, he plans to retake control of the world’s nuclear stockpile by having Felicity’s ex-boyfriend, Cooper Sheldon (Nolan Gerard Funk), hack against her code. Surprisingly, that may be easy for them this time as she’s not really on her game. Although she enlists the help of Curtis Holt (Echo Kellum) to help her and her outlaw father Noah Kutter (Tom Amandes) stop Darhk from regaining control, her mother’s arrival causes a distraction. Donna Smoak (Charlotte Ross)  doesn’t understand why Felicity would be cohorting with her deadbeat father, which forces her to confess that she’s been working with The Green Arrow for the past three years. After some more arguing between the former couple, things get real as Felicity’s ex makes his presence known to them through his code. 

Meanwhile, Oliver and Diggle chase a lead on Thea, which leads them to the bunker, which Ruve Adams, Darhk’s secret wife, calls the ark. They slip in undetected and find Thea tied to a chair. However, when they come to her she attacks them under the influence of the drugs. This forces Diggle and Oliver in a hasty retreat in which they hide out with a family in the town that’s devoted to the cause. 

Meanwhile, the combined efforts of Curtis, Noah and Felicity manage to repel Cooper’s cyber attack. By stopping him, they find a way to overload the system, shutting the villain out of his nuclear apocalypse, seemingly, for good. However, the bond between Felicity and Noah only sparks more tension between he and Donna. She eventually pushes him into an outburst where it’s revealed that Donna was the one who walked out on him, not the other way around. 

Back in the ark, H.I.V.E. soldiers eventually find Oliver and Diggle in their hideout. A fight ensues in which Thea catches up to her brother outside and attempts to kill him. However, he appeals to her humanity and begs her to remember who she is and not give up on the world above, no matter how potent the drugs in her system may be. Diggle finishes off the last of the soldiers inside the house but gets cornered by Merlyn. He’s saved at the last moment by Thea, who warns her father that if he drugs her again, she’ll kill him — a decision that’s questionable at best.

With the gang all back together, yet another new threat rears its ugly head. Somehow, Machin has forced his way into the ark’s control room. Surrounded by a slew of dead H.I.V.E. soldiers are his hostages, Ruve Adams and her and Darhk’s young daughter. He gives the villain 20 minutes to come rescue them or he’ll murder them both. Although it’s not our heroes’ fight, they can’t just let a woman and child die. 

With Darhk still unable to get word about what’s going on in the ark, the team arrives and confront Machin. However, the madman reveals he’s rigged the entire room with explosives, meaning if they fire an arrow it could set off bombs that would kill everyone inside the ark. Sadly, they’re forced to fire. Their attempts are futile, because the distraction posed by the first explosion gives Machin a chance to finish Ruve off. He escapes and the team grabs Darhk’s daughter and brings her to safety. However, the massive community underneath Star City is blowing up. Fortunately, there was plenty of time for people to get out, including the members of Team Arrow. Things cut to Merlyn, who is going to meet with Darhk. The villain has just heard about the loss of his wife and knows only that his daughter is missing. He mentions to Merlyn that he’s going to try to get control of the nukes again, to which the Dark Archer reminds him that, with the ark gone, there’s no safe place on earth if he launches the nukes. 

“Then let it burn,” he says. 

The episode ends with the villain storming through the door of the people who ruined his apocalypse plans, Felicity, Curtis and (to a lesser extent) Donna. He demands a favor, but odds are good that the Team Arrow members won’t comply so easily.