Bad To The Drone Carter is concerned when Zoe takes a part-time job at Cafe Diem but bigger worries await. Henry Deacon may face a long jail term for the breach of security that saved Kevin. Nathan Stark proposes to Allison Blake. Zane Donovan, Fargo and Larry are preparing for an anti-missile test and the Department of Defense sends in Eva Thorne, a ruthless corporate fixer, to conduct a performance review of Global. The Viper test should be swift and simple. Several target drones, developed by Dr. Ethan Edison, will attack and the Viper will shoot them all down. It happens every time. The real source of tension at Global is Thorne. Only Larry, always currying favor, is happy to meet her. The test begins and all the drones go down but one. It survives the attack; fires back, then cruises off into the sunset. None of the fail-safes can correct its course. Capturing it becomes Carter's assignment. He consults Dr. Edison who is baffled by his creation's success. "Martha" is a learning computer and she appears to be learning too fast. She should be a toddler but she is acting like a teenager. He worries about what she will do if she feels threatened. What she does is chase Carter into the Sheriff's office and promptly become invisible. Carter and Jo manage to corral her in the jail cell but their triumph is short-lived, as is the cell's back wall. Carter and Allison go to Edison's lab and meet his wife Mina, who is about to celebrate his success. Edison tells them that he did not give Martha the ability to cloak because it draws too much power; she will have to return to his lab to recharge. She is lurking nearby and sees Thorne, Stark and several others from Global confiscate Edison's remaining drones. Martha and Zoe share a teenage moment in Vincent's fusion-powered freezer before Martha liberates her fellow drones and leads them skyward. Thorne scrambles the fighter jets and, as Carter, Stark and Allison advocate tough love, the jets close in for a deadly confrontation in the skies over Eureka.
What About Bob? A scientist somehow vanishes from a sealed biosphere, prompting Carter and Allison to investigate. Meanwhile, the "Fixer" attempts to make Eureka's efforts more profitable.
Best In Faux The town's annual dog show segues into a canine malfunction; Zoe worries about the impact of the accelerated physics program on her life; earthquakes affect Allison's wedding plans.
I Do Over Events loop for Carter as he repeatedly experiences the same lousy day. Meanwhile, his free-spirited sister visits the town.
Show Me The Mummy A search for a mummy ensues after a famed archaeologist opens the tomb of an Egyptian queen at Global Dynamics.
Phased And Confused The emergence of a superhero makes Carter's job more difficult; Thorne's subterranean search for a secret beneath Eureka imperils Zoe and her friends.
Here Come The Suns The arrival of a second sun over Eureka upstages the town's mayoral race and forces Carter, Allison and Zane to investigate the fiery threat. Dean Marshall, Margot Berner.
From Fear To Eternity A scientific find produces sinister results and trust issues; Zoe's life is imperiled, and Eva Thorne knows the source of the predicament.
Welcome Back Carter Following his termination as sheriff, Carter interviews for a job with the Department of Homeland Security. Deputy Lupo resigns when she learns the new sheriff is a very personable robot.
Your Face Or Mine Carter takes a grueling recertification exam that tests him physically and psychologically; Allison pitches a town-wide DNA-monitoring security system to Henry that injures Deputy Lupo during the inaugural scan.
Insane In The P-Brane Objects become ambulatory after Dr. Tess Fontana reopens Section Five, which may be the work of poltergeists.
It Ain't Easy Being Green Long-term rivals from Area 51 visit Eureka for a bowling tournament; Carter probes an escalating series of pranks.
If You Build It... A strange structure comprised of electronics and scrap metal is assembled in a field by Eureka's teenagers, who appear to have been manipulated while they were sleeping.
Ship Happens Henry's ship returns, and Carter thinks it may be linked to the town's deadly electrical anomalies.
Shower The People Allison's baby shower yields eco-friendly gifts and the discovery of drowned scientists in an area where drowning is impossible.
You Don't Know Jack A sonic cleaning at Global Dynamics coincides with a phenomenon that causes Eureka's citizens to develop a communal form of Alzheimer's. Meanwhile, Allison goes into labor.
Have An Ice Day The arrival of an Arctic ice core causes the temperature to drop in Eureka on Dr. Tess Fontana's first day of managing Global Dynamics, and Taggart resurfaces.
What Goes Around, Comes Around Tess receives a job offer in Australia, Zoe is set to leave for Harvard, and Carter must contend with a magnetic disturbance that's floating above Eureka.