When Terra Nova comes under attack from a legion of Pterosaurs, Jim and Taylor must find a way to save the colony before it's completely overtaken. Elisabeth discovers a former flame is also living in Terra Nova and may have been responsible for her recruitment. Syke tries to make Josh feel at home and Reynolds get protective of Maddy.

When Elisabeth, Jim, Malcolm and Taylor investigate radio silence at a nearby scientific outpost, they discover an outbreak of a mysterious virus causing memory loss, paranoia and eventually death. The group must work together to find a cure before they lose their sanity and all of Terra Nova is infected.

When an orphaned "Sixer" girl comes to Terra Nova seeking asylum, Jim and Shannon are at odds if they can trust her; Mira plots to reclaim a valued possession; Taylor begins to suspect there is a traitor in his midst and Reynolds admits his feelings for Maddy.