Fargo is interviewing candidates for the upcoming FTL-powered mission to Titan. His former nemesis, now romantic interest, Dr. Holly Marten, is in town to help him, but he may have some competition for her heart in Dr. Parrish, whose application he summarily dismisses. Carter has other plans – he's hoping to take Allison and the kids on a fun, non-science vacation.
Jo is trying to strike a professional tone with Zane (their relationship has gotten physical) but Jo is doing all she can to shut down any emotional development. Zane has developed a special contact lens called PALs that allows the wearer to detect potential danger in any situation, factoring in mechanical as well as human features, and Jo is the first to benefit from them.
Carter follows suit, and when he speaks to Allison about the Titan mission, he detects that she is lying about not wanting to go. This falsehood comes moments after both of them find out that, in this timeline, she wrote the definitive book on space medicine. Additionally, though her headaches are getting worse, she refuses to see a doctor.
While at Café Diem, Jo and Carter detect a cataclysmic explosion thanks to their PALs, and though they don't yet know the cause, they know Zane's life is in danger unless they stop it. But before they can investigate further, the PALs malfunction – Fargo overloaded the system when he snuck a pair for himself in an attempt to impress Holly.
Zane and Henry work out a way to download any data the PALs may have captured and recreate the explosion scenario. They find that the explosion started at Global Dynamics, making the situation far worse than they originally thought. They begin evacuating the town and seeking the source of the explosion. Meanwhile Fargo puts Holly in charge of transporting the FTL drive to safety, just as the rest of the team realizes that the cause of the explosion is the massive generator powering the PAL system, which is on the verge of a meltdown.
Jo and Zane try to cool the system's core while Carter evacuates the holdouts – among them, Dr. Parrish, who won't leave without his life's work of highly nutritious space slugs. Carter realizes that the dormancy gel that Parrish uses to keep his slugs in top form could cool the core and save GD. Fargo reroutes the gel to the core, but the valves won't open. Jo must climb into the volcanicly hot pit and open the valve manually, but after she does so, her path back out is blocked by the hot steam. Zane jumps to her rescue, and reluctantly, she realizes that she may need to give Zane another chance.
As Fargo and Holly prepare for the interviews the next day, Fargo reveals that the PALs showed him that she would kiss him. But as the lenses were designed to detect security risks, she edges away post-haste.
Carter and Allison are unwinding from the crisis at home, where she tells him, truthfully, that she doesn't want to go on the Titan mission. But Henry, analyzing the remainder of the PAL data, comes across a frame that he must show to Carter: Allison was detected as a 99% security risk to GD.
We take you around the final day of shooting on the set of 'Eureka.'