The "Traveller In The Dark" turned out to be the episode we've been waiting for, but also dreading. Drill has a vessel.
A 4-year-old Minx wakes up screaming as Wes comes in to comfort her. He teaches her a new song, that will magically make all the bad stuff disappear: Twinkle, Twinkle Little Star. Quite the odd song to learn, knowing what lies in their future.
Wes and the Sec. of Defense are talking with Claire about the burn mark that Minx left on the child during the evacuation. As expected, this sends Wes into a tizzy; he just lost his wife and if his daughter turns out to have Drill possessing her, he'll lose Minx too. He asks Claire to talk to Minx to determine if she's still in there or if she's gone and of course Claire agrees. Minx plays a little bit of a mind game with her, making you wonder if Drill really is in her body. Jumping from one emotion to the next, it's hard to tell, until she coldly replies, "Shouldn't you have to prove I'm guilty?" The best way to do that is to have Minx touch Claire to see if she leaves a mark. They remove the rubber glove from Minx's hand, but she backs down from the potential revelation. Claire tries to find out what Orion is, but Minx still plays a mind game, before breaking down crying.
Sean and Rollins are speaking with the newspaper reporter, who thinks he knows what Drill is: a nuclear facility program. He couldn't be more wrong, but neither Rollins or Sean want to tell him that. Giving him the cold shoulder, the reporter up and leaves... as Sean changes his mind. Maybe the one way to get the kids home is to actually spill the beans.
Claire takes time to speak with her son about Minx, trying to get solid evidence that the little girl is indeed possessed. Henry swears up and down that it was Minx who grabbed the girl, further damning her. Claire then finds Silas, the paranoid child who was about to tell her who Drill was in the last episode, and he says that it was Minx who was in there when Benavidez died.
Wes, Claire and the Sec. of Defense get into Benavidez's computer even though it was fried. Of course, the last file she was working on with the incriminating evidence was altered... and it belonged to Minx. It's at that point Wes just absolutely breaks down, realizing that soon enough people are going to call for Minx's life, with Drill being trapped inside of her.
Sean and Rollins finish up telling the reporter the real story, which will essentially put the pressure on the White House to confess and in turn, free the children. There was an electrical device on the plane he was flying, and it was the thing that drew Drill to our planet.
Wes goes into the room Minx is kept in to talk to her. Her emotions keep bouncing around, but seem to come back to sadness that her dad doesn't believe her. It is very hard to believe her though, as one minute she's crying and the next she's playing a mind game. She begs her dad to get out of the room, she's innocent. He asks her to recite Twinkle, Twinkle Little Star... and she can't do it. Wes realizes that his little girl is gone and backs out of the room with Minx crying in the background, "You're my dad, you're supposed to believe me." Once she is left alone, she hears Henry in the room next to her and tries to get him on her side. They talk through the wall and she asks if they're friends, toying with his emotions.
Wes knows that they'll have to kill Minx, but he's hoping that she's still in her body a little bit so that she might be saved. He asks Claire what she thinks, is Minx dead? Claire doesn't know for sure and is left speechless, unable to help Wes in any way.
The Sec. of Defense speaks with the president and tells him that Drill is in Minx's body, something must be done. The president makes the extremely hard decision to take Minx out, using an electrical device that will not only kill Drill but more than likely kill any piece of Minx still left in her body. Shit. The Sec. of Defense sneaks into the facility and carts Minx away; Claire and Wes go to find the child and realize she's gone, causing Wes to have a next-level meltdown.
Claire speaks with Sean, asking if he knows a way to save Minx. He can't help and tells her that they spoke with the reporter, so Henry should be getting out soon.
The president finds out that someone spilled the secret, so he is indeed forced to go public with the information. He asks the Sec. of Defense how much time he has to do it, to which he replies 2 hours... just long enough to kill Minx. They decide to do a live press conference, and the circus begins. Wes talks to the president, trying to get more time.
Sean is still speaking with Claire on the phone when the reporter leaves... kind of. He tells Rollins and Sean that he got verification from the White House directly from Oberon. They're confused as to who that is, and the reporter explains that is the president's code name. The First Lady and their daughter Cassandra have code names as well: Olympia and... Orion. The child is Orion, aka Drill.
They figure out that Cassandra, the child who was burnt, staged the accident and framed Minx from the get-go. Minx is being carted on a hospital bed to a room where she'll be electrocuted and Wes is desperately trying to get back to the base to save her. It's a touching moment, as we see Minx being taken down a hall surrounded by guards, singing Twinkle, Twinkle Little Star to herself.
The Sec. of Defense sets the electric device into motion, with a tense 60-second countdown to keep the audience on their toes. Claire is trying to get through to the Sec. of Defense and Wes is banging wildly on the door, screaming that it's Cassandra who's Drill, not Minx.
Back at the White House press conference, Cassandra stands up and faces the cameras... and lets out the most horrific scream ever. The signal is sent.
The Sec. of Defense gets a call - there's a problem at the White House - and he cancels the electric machine just in the nick of time. Wes runs in to get his daughter and they have a moment; Minx never doubted that her dad would save her.
With the entirety of the White House, and presumably the world, recovering from the alien shriek, Claire comes up to talk to Cassandra. The child turns to her in a very calculated manner, and in a flat, lifeless tone says, "Don't worry, Claire... I'm not going anywhere."
Oh man, you guys are so screwed.