Carter and Allison's afterglow is interrupted by the continuing search for the DED device. At GD Henry discovers an anomaly in the fact that there's an area emitting no radiation - a natural impossibility. As he and Allison trace the source, Zane tells the others that he thinks Grant is behind the theft. To be on the safe side, Jo pulls Grant's original file from 1947 and she and Carter find some interesting items. They discover an audio recording Grant made regarding Carter in 1947, as well as a police report of the arrest of Beverly's father after he stole the plans for the bridge device. Carter realizes that if Beverly is involved, Allison and Henry are in danger. He rushes away and reaches them just as they discover a gorge where there used to be a plain.
Beverly, the thief of the DED device, reveals to Grant the method behind her madness: she needed the DED's plasma cell to power a new iteration of the bridge device that sent the crew back in time. Her plan is to send Grant back in time, ostensibly to right past wrongs, but also to keep her father out of jail. As they power up the device, a blast emanates from the gorge, which is the hiding place of Beverly's base. This occurrence sends Allison's SUV flying and Carter rushes to help her and Henry, but he's too late - Allison is dead. He discovers an entrance to the base and charges Grant and gets accidentally sent back in time with him. They arrive at Camp Eureka during the exact era that Carter, in his first time travel trip arrived at. Fuming, Carter tells Grant that his machinations killed Allison, and the two realize that they have an opportunity to save her life by convincing Adam Barlowe not to steal the plans for the bridge device.
After Adam refuses, Grant takes extreme measures by stealing the jumper cables that would've saved Adam's life, but Allison prevails in restarting his heart. Carter realizes there may be a way to save Allison without sacrificing anyone. He finds Grant's recording - the one he listened to in 2010 - and records instructions to his future self.
Fast forward to 2010, and Carter gets the message to rush to the gorge. He gets there in time to warn Henry and Allison, and though they sustain injuries, Allison lives. Carter rushes into Beverly's bunker, and he and Grant are replaced by their time-traveling selves: the plan worked, and they were sent back at the right time, but Beverly escapes.
Wrongs righted, Zane is released from the cell, and approaches Jo about why she had his grandmother's engagement ring. She denies everything, but Zane knows better when he sweeps her up in a kiss.
And Grant, compunctious after endangering Eureka, says his goodbyes and leaves Carter with a very special - a baseball autographed by Jackie Robinson.
Wormholes start popping up all over, threatening to rip Eureka apart unless Carter can stop them.