The sleepy Pacific Northwest town of Eureka is hiding a mysterious secret. The government has been relocating the world’s geniuses and their families to this rustic town for years where innovation and chaos have lived hand in hand. U.S. Marshal Jack Carter (Colin Ferguson) stumbles upon this odd town after wrecking his car and becoming stranded there. When the denizens of the town unleash an unknown scientific creation, Carter jumps in to try to restore order and consequently learns of one of the country’s best kept secrets.
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.
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.
Carter and Jo continue their search for the missing Astraeus crew. A surprising source confirms the new theory of the disaster, and offers to help them rescue the crew. Meanwhile, back at the lab, lives are at risk as more of the crew comes closer to the truth of their situation.
When a smart fire experiment gets out of control, Carter and team discover that the Astraeus victims may be the cause. Meanwhile, Fargo deals with Holly's death, Grace struggles to maintain her relationship with Henry, and Allison fights her feelings about Jo.
Jack starts to swap bodies uncontrollably, which puts both his body and his consciousness in awkward situations. Meanwhile, Warren Hughes returns to GD to evaluate Astraeus crew members' reactions to their abductions. Elsewhere, Zane's quest for answers from the Matrix reveals disturbing results for both him and Fargo.
It's disaster drill day at GD and everyone must participate in order to see how well they would do in a disaster. Unfortunately the computer conducting the drill makes the simulation a reality. Elsewhere, Fargo undergoes risky interfaces with the Matrix to confirm Zane's findings.
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.
While under the influence of a smart drug, Carter becomes a genius like everyone else in town and starts to change the laws of physics. Unfortunately, his condition soon endangers all of Eureka, including Allison's brother who is in town just to meet his new brother-in-law.
Jack and Allison's perfect honeymoon is interrupted when sabotage is discovered in Eureka. Elsewhere, Holly faces another hurdle to remain intact.
The Department of Justice arrives to investigate Grace, while Henry struggles with his conscience and 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.
In the series finale, wormholes randomly materialize around Eureka as the Department of Defense is set to shut the town.
Dr. Grant, a former resident of the town, causes serious alarm with his unexpected return. His romantic interest in Allison Blake also causes significant friction with Sheriff Jack Carter.
As the Founder's Day festivities continue, Carter and the others must accustom themselves to the new time line and how Dr. Grant fits into it. Unfortunately, re-acclimatization needs to occur on a steep learning curve.
Dr. Isaac Parrish, the brilliant director of the Non-lethal Weapons Lab, is feeling a little undervalued these days. Then all his latent hostility goes viral, infecting everyone with such fury that no one is safe, especially Fargo.
As Eureka celebrates Space Week, Dr. Ramsey unveils his cutting edge invention that could allow colonization of Mars. Unfortunately, a slight malfunction may cause it to incinerate Eureka before the dream is realized. Equally bad is that Eureka's go-to guy for crisis intervention has just gone to Boston to visit his daughter at Harvard.
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.
Carter's camping trip with Kevin becomes a little scarier than ghost stories by the camp fire when a malfunction with the AI at Global Dynamics may turn some of them deadly. Elsewhere, Henry thinks about telling Grace the truth.
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.
The gang begins seeing visions of people from their pasts, while the town seems to be collapsing around them. Meanwhile, Dr. Grant gets involved with a mysterious faction.
Dr. Grant attempts to return to 1947 but when Carter intrudes, they both wind up stuck in the past under the threat of altering present-day Eureka once again.
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. SYFY has this & "Of Mites and Men" Listed as episode 16 and does not have #17 "Clash of the Titans Listed"
Global Dynamics deals with two threats—a visit from Senator Wen and robotic bugs that can consume everything—it's unclear which is the bigger one. Meanwhile, Allison refuses to acknowledge any deficit with which the implants may have left her. SYFY has this & "Omega Girls" Listed as episode 16 and does not have #17 "Clash of the Titans Listed"
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 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.
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.
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.
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.
The town's mayoral race is disrupted when Zoe's science partner inadvertently causes a second sun to appear over Eureka.
When a potentially world-altering scientific discovery from Eureka's past finally comes to light, can anyone be trusted with it? The question is far from rhetorical for Carter: Zoe's life is in immediate danger and Eva Thorne knows why.
A new sheriff arrives in Eureka that turns out to be a robot that can change into human form (with mixed results). The town really needs the new sheriff as the town's gravity seems to be acting up.
Deputy Lupo stands in as the acting sheriff while Carter undergoes his annual physical, but she's not acting like herself.
Tess Fontana (Jaime Ray Newman) shakes things up in Carter’s world when she’s brought in by Allison to re-open Section Five.
A bowling tournament brings a rival science team from Area 51 to town, leaving Carter investigating practical jokes that escalate in scope and destruction as the competition progresses.
Teenagers construct an odd building in a Eureka field while asleep.
Henry's 20-year-old project returns with more on board than it left with.
Jack investigates the deaths of scientists who drowned in less than liquid circumstances. Meanwhile, Allison's baby shower goes green.
It's a busy day for Global Dynamics and Eureka as Allison's labor begins during a sonic cleaning of the company, and the townspeople exhibit Alzheimer's disease at the same time.
Tess hopes her first day in charge of Global will be uneventful; the arrival of an Arctic ice core brings a new Ice Age to Eureka