The season premiere of Eureka’s fourth season opens with the town getting ready for Founder’s Day. Allison asked Carter to help her with the celebration. Which he agreed to do, but things went a bit weird while he was finishing his jog as he ended up on a muddy road. He flagged down a car driven by a man named Dr. Grant. Dr. Grant gave Carter a ride to Camp Eureka. Carter was stunned to see that where the town should be was actually a military base. The Major in charge of the base cracked him on the head and knocked him out.
Carter woke handcuffed to a hospital bed. As the Major left Allison came over dressed as a nurse and helped Carter get free. Allison explained that they were both back in 1947 before Eureka was actually a town. As Carter and Allison tried to leave they see Jo racing from Military Police on a motorcycle. She is caught and taken into custody.
Allison told Carter to leave as she had to stay with a wounded soldier. Carter left and found Henry. Henry and Carter start trying to figure out why they were in 1947. The two of them find Einstein’s lab where a device was sitting turned on. Henry recognized it as the same as the one Allison’s son Kevin was messing with right before they went back in time.
Dr. Grant came in and found them. Henry and Carter explain the situation. The three of them came up with a plan they think will send them all back. Allison went to the stockade to see Jo, and found that Fargo was also in 1947. Allison helped Fargo and Jo get away but is caught by the Major herself. Jo and Fargo find Carter, Henry, and Dr. Grant working on the plan and told them that Allison had been caught.
Dr. Grant and Carter left to go rescue her. Dr Grant had Jack change jackets with him so he blended in more and to two rescued Allison from the Major. Dr. Grant told Carter and Allison to hide in the dance they were having. As time ticked down Carter realize he didn’t have his phone, he had left it in the other jacket. Allison told him to hold her hands and they should go together. As Carter kisses her for luck they transport back to 2010.
After getting back Fargo, Jo, Henry, Carter, and Allison realized there were a couple of small changes. They scattered to see if anything else had happened. Each found that a significant event in their lives had changed. Most for the good, some were not. We then see Dr. Grant in 2010 asking for Allison Blake.