Tess' reign as head of Global Dynamics may be shorter than planned after she receives an offer from Australia. Elsewhere, the town deals with a magnetic disturbance and Carter must come to terms with Zoe leaving for college.

The uneventful first day that Tess plans as the interim head of Global Dynamics is shattered by Taggart's reappearance and plunging temperatures caused by an ice core from the Arctic.

Tess begins a time capsule project for the town on the same day as Global Dynamic's annual sonic cleaning. Unfortunately, Fargo's attempt to erase history leaves some with a form of amnesia, and two people trapped in Section 5 with very little time to remember how to stop the cleaning – and no way to stop Allison's labor.

Carter investigates the deaths of scientists who drowned in less than liquid circumstances. Meanwhile, Allison's baby shower goes green.

Henry's 20-year-old project returns with more on board than it left with, and when a man is killed and another injured, Henry will have to face his past in order to save everyone's life. Back in town, Jo and Carter attempt to return the items from the towers to the owners with mixed results.

A wave of wholesale looting hits Eureka as the signal draws closer, and when the missing objects turn up in a field as part of five towers built by the town's sleep-building teenagers it becomes a race against time to find the cause. Meanwhile, Fargo breaks up with his car causing the AI to seek revenge after she's sold to Haberman.

When the bowling team from Area 51 hits town, the long-standing rivalry-cum-war is reignited, and a prank goes horribly wrong. Now Carter not only has to mediate between Area 51 and the home team to prevent more destruction, but also deal with the consequences of the first prank: a blob with an insatiable appetite. Elsewhere, Duncan returns to plead his case to a resistant Lexi.

When objects begin moving on their own, Carter and newcomer Dr. Tess Fontana visit the "other side" to find the answer.

It is time for physical exams for the Sheriff's department and an upgrade for the town's security system, both Eureka-styled by Global Dynamics. Acting Sheriff Lupo seems almost loopy after the 48 hour extreme exam, and she volunteers to a DNA scan for the new security system, but then a malfunction occurs.

Carter attends a job interview with the Department of Homeland Security. Deputy Lupo hands in her resignation on learning her new boss is a robot.

As Eva Thorne prepares to seal off the subterranean military complex, Zoe's life is endangered as her body begins to rapidly age.

The town's mayoral race is disrupted when Zoe's science partner inadvertently causes a second sun to appear over Eureka.

A mysterious "superhero" who can walk through walls is causing a ruckus in Eureka. Meanwhile, Zoe and her friends become stranded with Zane Donovan in an abandoned subterranean facility.

When an Egyptian tomb is opened at Global Dynamics, strange things start to happen, leading Fargo to believe it is the mummy's curse. The mummy, however, has disappeared, and Carter investigates.

On Allison and Stark's wedding day, Sheriff Carter finds himself stuck in a time loop, causing him to experience the same lousy day over and over again. Meanwhile, Sheriff Carter's sister Lexi visits Eureka.

The town's annual dog show gets into full swing—complete with exploding robotic canines. Meanwhile, Sheriff Carter experiences an isolated earthquake, Zoe contemplates quitting the accelerated physics program, and Allison starts fitting her wedding dress.

Sheriff Carter and Allison investigate the disappearance of a scientist from a sealed biosphere. Meanwhile, "The Fixer" attempts to make Eureka's ventures more profitable.

Eureka is threatened by an intelligent drone with "issues" after an anti-missile test. Meanwhile, Eva Thorne, nicknamed "The Fixer", after dismantling and rebuilding several corporations, arrives in Eureka to evaluate Global Dynamics' expenditures.