Regan tells Flynn what went down with Emme and says she lied to Finnerman and Jackson in order to keep Emme safe. Whew! Emme gets away with a "Stupid kid" and a slap on the wrist.
At the ETU, Steph figures out that Regan's father's last words were the Hunter alphabet and they can now translate the entire Hunter language to English, and vice versa. Finnerman wants to transmit an order to the Hunters.
The Hunters get a message from 'Bob Brecke' claiming that Musa says "The Purge is upon us" and they should go to a hotel in rural Ohio (the message, of course, was actually sent by The ETU to get the Hunters in one place). Musa knows it's a trap but he can't warn his followers since the ETU has shut down the Hunters communication system. Abby suggests they try to negotiate with the ETU through Flynn.
Jackson evacuates the hotel's guests and staff and replaces them with ETU members as Regan goes undercover to find out what the Hunters know about The Purge. Regan is weirded out to find that most of the Hunters showing up at the hotel seem like soccer moms and dads. She follows Hunter clicking sounds to the hotel room of a nice family. They are there because Musa called them for The Purge but confess they don't know what 'The Purge' means.
Flynn meets with Emme and implores her not to tell anybody what she knows about Abby. And then … Abby shows up! She begs Flynn to call off the round-up at the hotel, and then she drops The Big Reveal ...
The Purge isn't an attack. The Hunters are trying to leave earth and go home; they're purging the Earth of themselves, not humans. This is becoming like E.T., but even more extreme!
Flynn tells Abby that he believes her and they embrace. They both seem into it until he grabs her, points a gun at her head and tells her that he'll kill her if she lies to him again. Marriage.
Regan tells Jackson that the Hunters in the hotel aren't terrorists or extremists but innocent people going about their lives. Jackson remembers that Regan's father said "Protect the innocent ones" and goes to speak to Finnerman. Before he gets to her, Finnerman orders Briggs to lock down the 47 people inside the hotel. Regan urges the nice family to get out and helps them escape.
Outside the hotel, Flynn and Briggs surround a suspicious vehicle from which Musa emerges, wearing a suicide vest. He asks to see Jackson, his old CIA handler. He tells him that he's come to surrender but he must go into the hotel to tell his people to surrender as well. Jackson won't let him unless he gives up the location of his weapons but Finnerman allows him to go in if he removes his vest.
Musa enters the hotel and tells his people that they've been lured there like lambs to the slaughter, and he will set them free. Meanwhile, Finnerman reveals to Jackson that she plans to kill them all, including Regan, who "can't be trusted." Jackson cries genocide as Finnerman, as usual, poo-poos him. Jackson says he's going to pull Regan out and Finnerman has him ejected, ordering her soldiers to go in and kill all the Hunters. Regan gets a text from Jackson urging her to get the hell out of there.
The soldiers storm the hotel, enacting their brutal massacre. Regan tries to escape but gets shot as Abby and Musa hide in an upstairs room. Musa tears off some of his skin and burns it, emitting a gas that disables the human soldiers, including Briggs (neat trick!). Briggs' soldiers lose hearing and begin to keel over and vomit as the Hunters viciously counter-attack. Throats are torn out, naturally, though Musa himself is seriously wounded.
The episode ends with Flynn becoming disillusioned with this senseless killing and helping Regan escape. Time to go rogue!