The episode opens on Moira's press conference, set six months ago when she admitted to her culpability in the events of the finale. In the Glades, there's a prison where the guards don't evacuate, instead just taking the guns and running.
In his cell, Count Vertigo lives through the earthquake, shocked by its impact but freed by the damage it does to the building's infrastructure. He hands another inmate a ring of keys and wanders away, leaving the prison through a hole in the wall.
In the present day, Oliver is arriving at the courthouse with Thea, swarmed by the press. The district attorney and Laurel are discussing the trial off to the side, and Adam says he has a trump card Laurel doesn't know about.
On the island, Oliver is leading the crew of the Amazo to a campsite where he tells them that Slade and Shado are. Oliver calls out to them to warn them before the group fires on the camp. Shado and Slade aren't there anyway, but they set a bomb. Shado comes out of a hiding space and deactivates it after the group has moved on.
Diggle is looking ill as he's leading the Queens up the stairway into the courthouse, so Oliver sends him away.
In the courtroom, Moira sits down and shares a bunch of meaningful looks before the DA starts to present charges and Jean Loring gives her opening statements too.
At Queen, Felicity meets up with Diggle, who feints.
In a dark room, a man comes to find Vertigo; he tries to get more money out of Vertigo, who sticks him with a syringe, leaving him dead.
At the Arrowcave, Oliver shows up and they figure out that Diggle has been dosed with Vertigo and that the Count is out of the prison. He gives her an antidote he worked up and leaves to go back to court.
In court, the DA is going after Thea for not visiting Moira in prison, but after he finishes his examination, he collapses.
In the flashbacks, Ivo is looking for an object among the Japanese remains. He's looking for an arrowhead, but Oliver doesn't know where it is. He's thrown out of the plane site and they're threatening to torture him for the information when Shado and Slade show up with guns and arrows.
Back at court, Jean tells Moira that she has to testify since Thea's testimony went so badly. Oliver tells her that she doesn't have a choice--that whatever she's hiding can't stop her from trying to help herself.
At the cave, the news are saying that Donner collapsed with no warning. Diggle isn't doing well, still, but before they can get into too much, Vertigo takes over a TV signal; he's kidnapped Donner. He's somehow poisoned a number of citizens, and the only way to make the pain stop is taking Vertigo.
Kate Spencer meets with Laurel, telling her she's now lead counsel in the Queen case as long as Donner's missing. Laurel, looking thorugh his notes, finds his "trump card."
Back at the club, Roy comes to see Thea, giving her a pair of boxing glove and telling her to hit him to get some of her aggression out. Eventually she goads her into doing it, and she starts to get really aggressive with him until she's crying and he holds her.
Back at the cave, Oliver and company figure out where Vertigo is, and Ollie leaves to go after him.
At the prison, Laurel braves the threat of disbarment to talk to Moira, telling her it's a family matter. She says that she knows Moira is being called to the stand and that she can't testify. She says she'll have to ask her about what's in a file that she hands over, saying that it will jeopardize not only Moira's case but her relationship with Ollie and Thea.
At the abandoned city building where Vertigo is headquartering his drug manurfacturing facility, Arrow shows up. Vertigo uses human shields and his knowledge that Arrow doesn't kill anymore against him, but Ollie just blows up some propane tanks, torching the drug supply and taking out a couple of mooks before leaving with Donner.
In Loring's office, Moira tells Ollie and Moira that she had an affair with Malcolm Merlyn. The show cuts between her telling Oliver and Thea and then being interroggated by Laurel in court. Laurel is trying to convince Moira that Malcolm wasn't a threat to her and she wasn't acting under duress. Outside the courtoom, she sees Oliver and runs away. Ollie chases her down to see if she's okay, and she doesn't understand how he can forgive her. She walks off.
Back on the island, things are starting to get violent between the two groups of survivors; Ivo and his people release Oliver to Slade and Shado; Oliver grabs Sara as he runs and all hell breaks loose. The four of them are running from the captain and a couple of gunmen and the charge the captain had left on the campsite, now left on the ground as a mine, blows up right next to him.
In the present day, Diggle is still struggling at the cave; they figure out that the Vertigo dosages were distributed to people via a traveling flu shot truck.
Felicity leaves Diggle behind and goes looking for the truck, finding it evacuated. SHe starts going through cabinets, finding the Vertigo but then being discovered by the Count.
Jean shows up to tell Oliver and Thea that a verdict will be in soon; Ollie receives a call from Felicity but it's Vertigo on the other line. He's got Felicity tied up and has figured out who Ollie is. Oliver darts off in spite of Thea's protests. Arriving at Queen Consolidated, Ollie finds Vertigo and Felicity in his office. Vertigo tells him that he's being bankrolled by a man of means who also hates Oliver, and takes a few shots at Ollie, breaking up some glass in the office. Out of bullets, Vertigo holds Felicity hostage with a syringe, telling Ollie to drop his bow. He drops the arrow and lowers his bow, but when Vertigo goes to inject Felicity anyway, Ollie puts three arrows in him and sends him tumbling out a window onto the street below.
Back at the courthouse, Oliver finds Thea waiting where he left her; the jury is still not in. He tells her that something happened at work that he couldn't not be there for. Jean comes out to tell them that the jury is back. Moira is found not guilty, to the surprise of seemingly everyone. Laurel leaves without a comment. Back at the Arrowcave, Oliver knows that she should have been convicted--that the verdict doesn't make sense. He came to check on Diggle and Felicity. Queen's applied sciences division was able to synthesize a treatment for the tainted vaccine. Before he leaves to go home, Felicity thanks him for saving her and apologizes for putting him in that position. Oliver tells her that there was no choice involved; Vertigo had her and was going to hurt her.
Back on the island, Shado has the coordinates for the submarine on the back of the arrowhead. They plan to use the Miracle to save Slade. Ivo kills the injured Captain for having failed to stop Oliver and his group.
At Blood's office, he reveals that he's the one who was responsible for Vertigo's attack on Arrow, is called to the other room. A number of his Miracle test subjects are dead in chairs but Cyrus Vanch is alive and feels "stronger."
EDIT: A commenter below notes that's probably Cyrus Gold--better known as Solomon Grundy--not Cyrus Vanch.
As Moira is being escorted out of the courthouse, her driver says he's been instructed not to take her home yet. Bringing her to a parking lot seemingly in the middle of nowhere, the driver is shot through the heart with a crossbow bolt; it's from Malcolm Merlyn, who faked his own death and rigged her trial. He also learned that Thea is his daughter.