The Astraeus crew returns to Eureka four years later and must adapt to a myriad of changes, including a more oppressive version of Deputy Andy. (TV Guide)

Carter and Andy are jailed for trying to steal a piece of equipment to complete a device that Kevin has assembled to search for the Astraeus crew. Meanwhile, Holly comes up with a dangerous theory. (TV Guide)

Beverly Barlowe resurfaces in Eureka seeking Carter's help to free the Astraeus crew, and the rescue plan lands Carter in the crew's virtual world. (TV Guide)

Fargo deals with Holly's death; Zane and Allison evaluate their romantic relationships after their experiences in the virtual reality; a project threatens to ignite the town. (TV Guide)

D.O.D. psychological assessor Warren Hughes resurfaces, and Carter begins to exhibit strange behavior. (TV Guide)

A disaster-preparedness drill for Global Dynamics goes awry and imperils the town. Meanwhile, Zane participates in a secret simulation for Fargo. (TV Guide)

Fargo thinks Holly is alive in the virtual Eureka, but a security program hampers efforts to retrieve her consciousness. Meanwhile, Carter is linked to seemingly paranormal activity at Global Dynamics. (TV Guide)

A submarine mishap ruins a romantic outing for Carter and Allison, and Jo must sort through pranks at Global Dynamics to save them. (TV Guide)

Allison's brother visits to meet her new husband; Carter's intelligence mysteriously begins to grow exponentially. (TV Guide)

Carter's honeymoon with Allison is complicated by saboteurs in Eureka. (TV Guide)

Eureka is cut off from the world by a malfunctioning experiment that threatens to eradicate the town's populace. (TV Guide)

The town's communications systems go haywire because the SmartDust control unit is broken. Meanwhile, the bio-printer vanishes; and Holly behaves strangely. (TV Guide)

Wormholes randomly materialize around Eureka as the Department of Defense is set to shut the town down. (TV Guide)