An accident leads a U.S. Marshal and a teenage girl (who later is revealed to be his daughter) to a peculiar town populated by scientists and their families where 10-year-old boys are in 11th grade, the local diner doesn't believe in menus, and E=MC² was just the beginning. Just as the Marshal starts to get settled into the swing of things, a local scientist develops a bomb that seems to appear anywhere and eats all the matter around it.

The citizens of Eureka attend the funeral of Susan Perkins, only to find out that she is in fact alive. Meanwhile the Sheriff moves into an underground bunker that is actually a 'smart house' controlled by a computer dubbed 'S.A.R.A.H., and begins to investigate a 'ghost' that has been appearing in town.

Something starts to steal the townspeople's memory...

After hosting a movie party, Spencer is found the next day in the middle of a crop circle, claiming he was abducted by aliens; and then other people who attended the party start to go missing as well. Elsewhere, the legislator responsible for Eureka's funding visits the town, and gets dragged into a Sector 5 experiment...

An unpredictable researcher accidentally unleashes a dangerous artifact which was previously hidden by Nathan Stark.

A sleeping weapons system is accidentally awakened by Fargo and Spencer. Henry tries to avert the pending catastrophe with the help of a retired, nonsensical scientist.

Carter investigates an unusual car accident. Meanwhile, Stark, under the stress of completing a project on time, pressures two research teams to produce results.

A former resident returns to Eureka and creates mayhem which threatens Global Dynamics, prompting Stark to take action.

Taggart achieves a medical breakthrough while Fargo invents a device that bridges the divide between computers and human brains.

Strange behavior exhibited by the townspeople is investigated by Carter,who has to solve the mystery before Stark makes a decision that could affect the world.

A bad day in the lab forces Carter to rethink his decision to live in Eureka, prompting an intervention from S.A.R.A.H. (the self Activated Residential Automated Habitat.

Ambition trumps common sense when Stark is given a chance to try out the Top-secret artifact. Once it's tested, Eureka warps into the future and ends up in 2010, where the town is different.

Taggart's theory is that solar flares caused by the eclipse, or the 'Phoenix Effect', are to blame when people start to spontaneously combust. When Carter discovers that a blast of radiation from the artifact had penetrated the wall of the chamber and is actually to blame for the spontaneous combustion, it becomes a race against time to save the other two people exposed - Nathan and Kevin!

Fargo accidentally triggers a prototype for a personal force field, which goes out of control, forcing Carter to enlist Stark's help.

Dr. Whiticus creates an incredible "weather machine" intended to reverse the effects of global warming which instead stirs unexpected results.

Carter suffers a blow to the head, and after arguing with Zoe, he suddenly finds himself in a parallel Eureka, where the residents seem to be mysteriously vanishing.

Falling space debris threatens Eureka residents and Carter turns to high school science fair participants to solve the problem. Specifically, he taps a student science project created to harness the sun's energy. Also, Zoe gets an eco-friendly automobile.

One of the Global Dynamics tanker trucks spills, potentially causing a change in everyone's sleep habits... In the course of the episode, we come to learn that Global Dynamics has developed a technology that enables them to distill six months of the town waste and by-products into one truck, an amount that would normally fill Lake Erie.

Fargo's grandfather awakens after 50 years in cryogenic suspension and accuses his rival of putting him there and stealing his work.

As an experiment that will recreate the first moment of the origins of the universe, the Big Bang, goes terribly awry, the town’s geniuses turn into morons, leaving the fate of Eureka in the hand of Jack Carter and an antisocial young ubergenius.

An abandoned research project on invisibility returns to haunt Eureka. Carter and Zoé become tangled in a web of strange occurrences that lead to Carter’s disappearance and the possibility that he might never reappear.

Sudden muteness, human bioluminescence and faucets running blood cause many of Eureka’s citizens to believe that they are the victims of a biblical plague.

Sheriff Jack Carter becomes absolutely irresistible to every woman in Eureka. But if he doesn't get his mojo under control, they might just eat him alive.

Beverly Barlow returns to town just as a parasitic bacterium threatens to destroy Eureka, by turning everything to gold and then into rust --- people included.

Nathan Stark and Jack Carter must put aside their rivalry to stop a deadly bacteria from destroying the town and killing Allison’s son. But can Carter ignore Stark’s crimes, as well?

The search is one for an escaped drone as Eva Thorne arrives to assist the clean up of damages which Global Dynamics has caused.

Carter and Allison investigate when a scientist mysteriously disappears from a sealed biosphere. Meanwhile, the "Fixer" tries to make Eureka's efforts more profitable.

Eureka's annual dog show is underway and is like none other. Meanwhile, Sheriff Carter experiences an earthquake; Zoe debates quitting the accelerated physics program; and Allison starts the process of fitting her wedding dress.

It's Allison and Stark's wedding day and Carter finds himself reliving it over and over. Meanwhile, Carter's sister, Lexi, visits the town.

A search for a mummy ensues after a famed archaeologist opens the tomb of an Egyptian queen at Global Dynamics.

Carter's job is made more difficult when a super hero emerges. Meanwhile, Zoe and her friends are imperiled when Thorne makes a subterranean search beneath Eureka.

The Eureka mayoral race is overshadowed by the sudden arrival of a second sun, forcing Carter, Allison and Zane to investigate it more closely.

Trust issues are produced by a scientific find, along with sinister results. Zoe's life is in jeopardy, and Eva Thorne knows what has caused the predicament.

Carter interviews for a job with the Department of Homeland Security, after being terminated as the sheriff. Deputy Lupo decides to resign after discovering that a very personable robot is the new sheriff.

Jo displays atypical behavior after a DNA scan malfunctions, unfortunately it's while she's interim sheriff because Carter is undergoing a 48-hour DOD recertification test.

Dr. Tess Fontana reopens Section 5, causing objects to become ambulatory , possibly due to poltergeists.

Carter finds himself chasing down creation of blob-ical like proportions when a series of escalating pranks turn deadly. Elsewhere, long-term rivals from Area 51 come to Eureka for a bowling tournament.

Eureka's teenagers who appear to have been manipulated while asleep, gathered in a field where they assembled a strange structure comprised of scrap metal and electronics.

Henry's ship returns causing Carter to fear it maybe linked to the town's deadly electrical anomalies.

Allison's baby shower fetches her a load of eco-friendly gifts and the discovery of a drowned scientist in a location where drowning is impossible.

Global Dynamics sonic cleaning coincides with a phenomenon in which the citizens of Eureka develop a form of amnesia. Meanwhile, Allison goes into labor.

The first day on the job as temporary head of Global Dynamics proves daunting for Tess when a new Ice Age comes to Eureka; and a familiar face returns in the process.

Tess has a job offer from Australia, Zoe is prepared to leave for Harvard and Carter has a magnetic disturbance above Eureka to contend with, in the third season finale.

It's Founder's Day in Eureka and everyone is in the spirit of the celebration until Jack, Allison, Henry, Jo and Fargo are transported back to 1947 where they meet some familiar faces along the way. Will they be able to get back to 2010 or will they be stuck forever in 1947 where Eureka is not a town, but an Army base.

When the 5 get back to their time, things are changed everywhere. As the Henry tries to fix the machine that transported them in the first place, Dr. Grant is making himself comfortable as he can. Jack is still trying to wrap his mind at the fact that he asked Tess something that she says yes to and the fact that the group's positions changed. As one thing leads to another, a twist happens and things get a little dicey.

When a prototype sets everyone into bad temper mode, the issue escalates and gets worse beyond the control of what Jack can handle. As Jack and Allison and Tess are the only sane people at Global Dynamics they have to devise a plan that will make everything calm and happy again. Meanwhile, Henry is helping Dr. Grant re-build the bridge that got them back to the new world except everything they touch disappears.

It's space week in Eureka, and everyone is gearing up for the rocket race - except for Carter. General Mansfield is in town for the big Race to the Moon, and is debriefed on a new oxygen-generating fluid designed, called TAP, for colonizing Mars. When the question about someone using TAP to fuel their rocket, the whole town of Eureka is in danger and it is up to Kevin to save the day this time. Will he do it, or will Jack come back to see charred remains of his friends?

Claudia Donovan visits Eureka to see if Fargo's promises of wondrous devices are true, but she finds herself in the middle of a mystery suitable for Warehouse 13 when objects begin to appear randomly around the town and GD, and it must be solved before there are deadly consequences.

When Sara gives Andy a (as Zane calls it ) an EMO download to give him emotion, she inadvertently affects all Level 6 AIs. Including Tiny. She escapes while being transported to NASA and is on the loose. Meanwhile, Jack takes Kevin camping with Fargo and Grant and Jack is not happy that Grant is there. They argue on who is with Allison and who is not and they are interrupted by Tiny who has an attachment to a certain object of Kevin's.

Love is in the air as Carter gets fed up with Grant's pursuit of Allison, Zoe conceals her love and Henry courts Grace. But all the emotions may have to be put on simmer when people in town start turning to stone.

Eureka's citizens face the return of people from the past; Global Dynamics tests a new device.

When Grant and Carter become stranded, they must race back in time to save Eureka.

Carter can't get into the Christmas spirit especially with the town surrounded by a force-field. Fargo organizes the GD holiday party, and Allison is full of holiday cheer.

Zane pesters Jo for details she does not want to reveal. Carter problem-solves at Andy and S.A.R.A.H.'s wedding. Elsewhere, Zane's actions make him and Fargo unexpectedly airborne.

Carter's duties expand to babysitting when Allison attends a medical conference, and Fargo finds his groove when a certain song is played. Meanwhile, a rocket scientist appears at Café Diem.

Jo receives a technical boost to her crime-fighting ability with lenses that predict security breaches. Allison's headaches won't go away so Carter plans a vacation. Fargo, meanwhile, deals with an onslaught of volunteers when he announces a space mission with room for civilians.

Jack deals with a bank robbery which may relate to the sudden gravity issues besetting the citizens of Eureka. Meanwhile, Fargo's rivalry with Isaac Parrish is boosted when he learns Holly and Parrish went on a date.

When Zoe comes home for a visit, Jo faces an angry woman who doesn't accept her fumbling explanations about Zane. This all fades to background noise, however, when they find everyone in Eureka unconscious and must find a way to work together so they can revive the town and beat Beverly before she gets hold of valuable data.

When mites threaten to take down Global Dynamics, Jack is called into action since Jo is in the middle of training. Allison is struggling with the fact that everyone things that her brain doesn't work and she is determined to prove that she is back in action again. 

The Eureka atmosphere becomes toxic when Department of Defense auditor comes to assess the team's relationships.

The Astraeus candidates go through their final interviews while Carter and Allison appeal their relationship audit.

When an explosion in the Astraeus lab accidentally sends Andy to Titan the team must devise a plan to save him before it's too late! Eureka

In the season finale - It's chaos in Eureka when an energy beam rips through main street but the Astraeus launch must go on...with or without Eureka intact.

The quaint town of geniuses is transformed into animated versions of themselves. Sheriff Carter and Allison Blake are secretly planning the perfect holiday surprise for their kids. But a mysterious kaleidoscopic wave of color crashes over Eureka, leaving the entire town and its inhabitants animated.

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.

The town huddles in a last attempt to locate the vanished Astraeus before it's too late!

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.

When a smart fire experiment gets out of control, Carter and team discover that the Astraeus victims may be the cause.

The crew moves forward after an ordeal and Warren's visit adds to the pressure.

Henry conducts a preparedness drill that winds up a disaster and Fargo faces a hard reality.

Fargo is convinced that Holly is still inside of the Matrix computer, but the DOD is determined to wipe its hard drive clean -- losing Dr. Marten forever.

Carter's romantic surprise for Allison turns deadly when they're trapped in a sinking marine lab with time and oxygen quickly running out.

When Allison's genius older brother comes to meet her new husband, Carter feels the pressure of not being smart enough to measure up.

Jack and Allison's perfect honeymoon is interrupted when sabotage is discovered in Eureka. Elsewhere, Holly faces another hurdle to remain intact.

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

The people of Eureka are being kidnapped and replaced by body-doubles one by one unless Allison, Fargo and Zane can figure out how to avoid capture and save their town.

Wormholes randomly materialize around Eureka as the Department of Defense is set to shut the town.