Let's start with events from the Sideways World this week, as no one character was the focus:
A lot of action took place in the same building. Claire arrived there to speak to an adoption agency, only to run into Desmond. He pressured her, in a nice way, to talk to a lawyer from of his that was also located in the building. This turned out to be Ilana, and it also turned out that she was looking for Claire. We soon found out why when Jack and his son, David, also arrived at the building.
They were there to listen to Jack's dad's will - and, as luck would have it, to meet Claire. Jack knew she was in the will, but didn't know why until tonight. He was taken aback by the news that Claire is his half-sister, but then had to reschedule the will reading because he was needed at the hospital. David went with him and wished his dad luck before the surgery, seemingly giving him extra confidence. Inside the OR, Jack said he thought he recognized the patient: John Locke.
Earlier, Sun had been brought to the same hospital and freaked out when she saw Locke in a gurney. "That's him," she yelled. She'd eventually undergo surgery and come out of it okay.
Meanwhile, Sawyer briefly chatted with Kate at the police station, as they awaited the FBI to arrive. But then he left when Miles told him about the shooting at the restaurant. They had Sayid on security camera and went over to arrest him at Nadia's.
On the island...
Fake Locke took Jack aside and admitted that he had pretended to be his father on the island, but only for his and everyone's best interests. He wanted to get them off the island. Jack didn't really know what to do and was taken aback when Claire later said Jack had no choice, he was "with" Locke because he had talked to him. But Sawyer had another idea: soon after Zoe came by the camp and said Locke better return Desmond by night fall, and Locke reacted by telling the group it was time to head to Hydra Island, fight Widmore's people and get on the plane, Sawyer told Jack to gather Sun, Hurley and Lapidus.
He and Kate were heading to sail a boat around and pick up Locke and the other castaways, per Locke's orders, but were gonna head to Hydra instead and get on the sub. Jack agreed. During the walk with Locke and company, they snuck away, but Claire saw and followed.
They had the chance to because Locke ran off to check on Sayid. He found him and asked if he had carried out his order: kill Desmond. We saw the exchange between these two and Desmond, stuck in the well, asked Sayid: If you do see Nadia again, what will you tell her you did to make it happen? When Sayid sees Locke, he says he carried out the killing demand, but it's clear he's lying. Can he really be brought back from the dark side?
Meanwhile, Jack, Sun Hurley and Lapidus find Sawyer and Kate on the boat. But Claire holds them all at gunpoint. Kate is able to talk sense into her and gets her to come. All good, right? Wrong. During the ride, Jack tells Sawyer the island isn't done with them. If Fake Locke wants them to leave, they should clearly stay. Sawyer bristles at this notion and tells Jack to get off his boat. Jack does. He jumps off and swims to shore. When Sawyer and everyone arrive at Hydra, they are met by Zoe and Widmore's people, carrying guns.
And also by Jin. We get our long-awaited Jin/Sun reunion, but it's very short-lived. Zoe talks to Widmore on the walkie and then orders our castaways to get on their knees. She says the deal is off. She radios someone to fire away - and an explosion takes place on the other island, where Jack just swam ashore and ran into Locke and the Others. Everyone else seems to die, but Jack is just knocked silly.
He gets carried away by Locke, who ends the episode by telling Jack it's all gonna be okay. He's with him now.