On the Destiny, some of the crew are being affected by hallucinations so strong that it’s affecting their judgment and impairing their day to day activities. Lt. James hallucinated that Lt. Scot has sex with her and then leaves her behaving rudely saying that he cannot be with her. She demands that he chooses between her & Chloe but he brushes her away. She lifts a lamp and hits him on the back of the head with it and is horrified that she has killed him. Dale Volker who has claustrophobia is unable to open the door to his quarters and starts yelling. As others later open the door he chalks it off as a simple malfunction but in the hallway he finds himself trapped within walls that didn’t exist a while back.

Lt. Scot imagines that he sees his son Matthew running in the hallways and chases after him. Dunning starts scratching at an itch and gets panicky feeling that a snake is inside him and is cutting himself to get it out. Greer imagines that he sees Wray conspiring with other civilians to take over the ship and starts to spy on her. Rush sees shadows but when he approaches it there is no one there. As TJ examines the ones affected it soon becomes apparent that the ones affected have all been on a planet recently and suspects that something affected them there. Just then, T.J. radios Young, telling him she has found the cause. T.J. presents Young with what she has found; a tick-like bug is embedded in Scott’s scalp, just above the back of the neck. She passed it over on her first examination because it is so small. T.J. speculates that the ticks inject a venom causing the hallucinations, and believes that removing them is the way to solve the problem. Scot is first to go and he reacts violently at first. The tick goes from him and jumps onto Chloe, who while passing another section of the ship sees her dead father.

Meanwhile Greer sees Wray & Rush talking privately and says that he will not let the two of them conspire to take over the ship. It is Eli who finds Chloe talking to what she thinks is her father. Rush finds himself in a tank filling with water and then suddenly he is out of it but sees a blue alien stalking him. Using the venom from the squiggly alien, TJ is able to remove the ticks from the others and they are killed. Rush prevents Greer from killing Wray, although she gets a deep wound. Scot then subdues Rush who is still seeing more blue aliens and TJ clears everyone from the ticks. As the episode ends, Destiny drops out of FTL and dials to a planet that seems habitable. Young decides to send out a team, not letting the tick incident deter him. He radios Scott and orders him to ready his team.