Scott finishes having sex with James. When he's done, he tries to leave and James demands that he choose between her and Chloe. When he tries to brush past her, they struggle and Scott throws her to the floor. She smashes him in the head, killing him.
Volker tries to leave his quarters and discovers that the door won't work. He tries to call for help on the radio but no one answers, and no one responds when he pounds on the door. Riley finally comes in and, disgusted, demonstrates that the door is working fine.
Greer is walking the corridors when he notices Camille working on her computer in the Gateroom. He wonders where everyone else and she says that there was no one there when she arrived. Greer asks what she's doing and Camille says that she's updating the personnel files. She says that Rush and Young know what she's doing. As she walks away, Eli comes by and asks Greer if he's seen Scott.
James is in her quarters watching Scott's corpse when Young calls her on the radio. She responds and says that she's been distracted and forgot her assignment.
In the mess room, the soldiers are discussing the fact that Young called off the search for Franklin. One of the men, Dunning, clutches at his arm briefly before going.
Volker is walking down the corridor when he finds his way blocked by piping that has never been there before. He turns to retrace his steps but finds the way back blocked. Scott, alive and well, calls out to him and Volker discovers that he's suddenly in an unblocked corridor. Scott suggests he should go lie down and Volker agrees. As Scott walks away, he sees a figure run down the corridor. He goes in pursuit and sees his son, Matthew, at the end of the corridor.
Rush goes to see Camille and says he needs to talk to her about something he just saw. Young comes in, interrupting them, to ask about what Greer said. Camille denies ever being in the Gateroom, but Young notes that Greer has reason to doubt her after the mutiny.
Scott chases after Matthew and runs into Chloe. There's no sign of the boy and Chloe hasn't seen him. They get a call from the work-out room that there's an emergency. When Scott gets there, Dunning is trying to cut something out from his arm, thinking there's a snake inside. As Scott helps subdue him, he sees the boy again in the doorway.
Johansen checks Dunning afterward but can find no sign of any contamination or parasitical infection. Young tells Johansen to keep the man under observation. Meanwhile, Eli and the others discuss the situation in the mess room and Riley wonders why more people aren't cracking up, given all the stress. Eli admits that he's relieved that the soldier didn't start shooting people. Chloe notices that Greer is staring intently at Camille and Rush, working together. Greer snaps out of it and says that he's fine.
Later, Rush is working alone in the control room when he hears someone behind him. Figuring that it's Greer, he goes out into the corridor and tells him to show himself. Brody comes by and wonders who he's talking to, and Rush dismisses it as a mistake.
Volker is in his room trying to rest. He suddenly fines himself confined in a cramped space with no escape.
Scott finds Matthew again, but he just turns and walks away.
Young tries to contact James but gets no response. He goes to her quarters and finds herself sitting on her bunk, sobbing. She apologizes but there's no one in the room.
Scott approaches Matthew on the observation deck and insists he can't be real. The boy asks why Scott left him. Crying, Scott gets a radio call asking him to come to the infirmary. When he arrives, James is startled to see him alive. Scott admits that he's hallucinating as well. Young points out that everyone suffering was on the last away team. Volker and Corporal Barnes were also on the mission. They go to get Volker and hear him screaming.
Barnes tells them that she isn't suffering hallucinations, and Johansen can't find anything wrong with her. Young orders quarantine and discusses the matter with Chloe. He assures her that there's nothing she can do and that the situation has been contained. Johansen calls Young to the infirmary to show him that he's found tick at the top of the neck on all of the victims except Barnes. Volker starts to panic again and Johansen gives him a sedative. Scott volunteers to have Johansen try and remove the neck in the normal manner. He sees his son again and quickly agrees. However, when Johansen touches the tick, he convulses and passes out. They manage to revive him, but Johansen discovers the tick has dug in even deeper.
Young orders Johansen to find another way to remove the tick. James, looking on, hallucinates that Scott is covered in blood.
In the corridors, Greer secretly watches Camille as she appears to sabotage the ship.
As Chloe walks by the shuttle bay, she sees someone seated inside the shuttle. Going in, she finds her father waiting for her. Senator Armstrong says that it's okay and asks if she's happy to see him. He admits that he missed her and hugs her.
Greer sees Rush and Camille conspiring and confronts them. They insist they were just talking, and Rush tells him to say what he has to say. He warns them that they're not going to take over the ship, and they insist that he's paranoid. Rush brusquely dismisses his concerns and they both walk off, Camille smirking.
Chloe explains their situation to her father and how she's talked to her mother. He's proud that she's able to explore the galaxy and see new things.
Johansen explains to Young that the anesthetic she used to save Rush might sedate the tick long enough to remove it. Scott wakes up and Johansen determines that the tick has disappeared. The ones on the others are still there, and they wonder if it jumped.
Eli finds Chloe on the observation deck, apparently talking to herself. She insists that she's fine and that Senator Armstrong is here. Chloe knows that he's not real and tells Eli about the tick. He panics but Chloe insists that she's not suffering and she's in control. However, she doesn't want to lose her father again, and promises she'll go to see Johansen eventually. Until then, Chloe asks Eli to keep her secret and he agrees.
Rush is walking down the corridor and finally turns and tells Greer to step out. There's no sign of Greer, but Rush finds himself suddenly sealed off behind glass panels. Water fills his small chamber... and he snaps out of the hallucination.
Johansen and Young check everyone for ticks but don't find anything. They realize that Chloe was there earlier and Scott goes to find her.
Rush is in his quarters, trying to get a grip on himself, when an alien appears before him. He gets out and seals it in.
Johansen administers the anesthetic to the tick on James and removes it safely.
Rush calls Young on the radio but gets no response. Bracing himself, he goes out into the corridors.
Scott finds Eli, who directs him to Chloe on the observation deck where she's holding a conversation with her father. Scott wants her to come to the infirmary, but she denies having any hallucinations. Eli breaks his promise and Scott insists that she go. Chloe's father asks her to stay, but Scott and Eli pull her away.
Rush goes to the Gateroom and sees the aliens emerging from the wormhole.
Greer confronts Camille, who tells him not to tell lies about her.
The aliens spot Rush and approach him.
Greer sees what he believes is Rush and runs off.
Chloe tells Johansen that she wants to keep the tick, but Young tells Johansen to go ahead. The hallucination of Senator Armstrong tells Chloe that he loves her, and she's living his dream. He kisses her one last time and then disappears as Johansen removes the tick and smash it. Greer calls to tell Young that the civilians are planning another mutiny and he's in pursuit of Rush. Young orders him to stop, but Greer hallucinates Young ordering him to use extreme force and go on radio silence. When they wonder what's going on, Johansen suggests that they may have been more than one tick on each victim.
Camille follows Greer and tries to get her attention, but he ignores her.
Rush runs away from the aliens and hides in a storage room. He grabs a tool and prepares to attack Greer, believing he's an alien. The armed Greer calls for Rush to come out. Rush attacks what he believes is an alien, but is actually Camille. He stabs her in the shoulder, but Greer knocks Rush down and seals the storage room, and then prepares to shoot Camille.
Scott and his men try to find Greer, and discover that Rush and Camille have disappeared. Young goes to help and tells Johansen to be careful. Meanwhile, Eli talks to Volker, who speculates that the tick's venom enhances existing emotions. James glances at Chloe and says nothing about her emotions.
Camille asks Greer to get her medical attention, but he hallucinates more conversations with Young and receives orders to continue the interrogation. However, he advises "Young" that he should eliminate Camille and Rush.
Scott and his men track Greer to the cargo bay and hear Camille inside. He calls out and Camille warns him what's going on. Scott tries to get through to Greer without success, and prepares to blow the door open with explosives. Greer prepares to shoot Camille, and his father Reginald appears in the shadows, telling him to do it. Rush manages to recover enough to attack Greer, delaying him until Scott blows the door open, gets inside, and has his men subdue Greer. However, Rush goes berserk and attacks them and they're forced to knock him down as well.
Later, Johansen checks everyone and removes the remaining ticks. She figures that things will get back to normal, but Camille wonders what that means.
In the aftermath, James watches Scott. Rush looks nervously around. Camille passes Greer in the hallway and ignores him. Eli watches Chloe, standing alone on the observation deck, and turns to leave her alone.
At the next planet, Rush confirms that they have 10 hours and the planet has a breathable atmosphere. Young wonders whether it's safe to send a team, and finally figures their luck has to change sometime. He tells Scott to get a team ready.