Two Secret Service agents find themselves on opposite sides of the action during a presidential visit to a museum, which results in an encounter with the mysterious Mrs. Frederic and their transfer to a top-secret facility in South Dakota.
Bank robbers use a musical weapon to go on a crime spree. Pete and Myka chase down the thieves while Artie investigates a hacker who tried to enter the warehouse's computers.
Pete and Myka travel to a small town where the residents are slowly going insane due to the influence of an artifact. Meanwhile, the mystery hacker gets closer and closer to the warehouse's location.
A psychiatric patient, Claudia Donovan, kidnaps Artie and insists that he help rescue her brother... who is caught in an interdimensional void.
A mysterious thief uses an artifact to steal a Native American sculpture, and Pete and Myka must determine what the thief's ultimate goal is... and how to stop them.
An explosion in a St. Louis police station reveals the corpse of a Warehouse agent... and unleashes a potent artifact upon the world.
The agents are sent to Washington to recover a samurai sword that can render its wielder invisible. However, when the sword is stolen, they realize that a rival artifact collector is involved... and he has ties to Artie's past.
While doing inventory in the warehouse, Myka is unknowingly trapped in a mirror belonging to Lewis Carroll... and replaced by a mirror image psychopath who goes with Pete to Las Vegas to recover an artifact two conmen are using to win at the casinos.
When four prisoners commit suicide at a maximum-security prison in as many weeks, Artie sends Pete and Myka to investigate. Meanwhile, a frustrated Claudia decides to use an artifact coat to change a light bulb, and chaos ensues.
Arnie is summoned before his mysterious superiors, the Regents, who question whether he's following the rules. Meanwhile, Claudia accidentally sets off a catastrophe in Warehouse 13 and works with Pete and Myka to stop it before the system explodes.
While hunting down MacPherson, Myka receives word that her father is dying. She discover that he's the victim of an artifact, one that someone intentionally sent to him.
MacPherson manages to steal artifacts from the warehouse and put them up for bid. However, his scheme is part of a much greater plan, one that may potentially end in disaster for everyone.
In the aftermath of MacPherson's invasion of Warehouse 13, the team discovers that he has abducted another prisoner from the Bronze Sector. While Artie travels to Switzerland to find Claudia, Pete and Myka go to London to find the second prisoner: H.G. Wells.
A superpowered vigilante is at large in Detroit, and the agents try to track down the person responsible. Meanwhile, things between Leena and Claudia are still tense, and Artie is haunted by the spirit of his dead friend.
A lost artifact created by Philo Farnsworth falls into the hands of an unsuspecting Univille townsperson, who inadvertently uses it to start projecting 1940s movies that take on a life of their own... and the next feature involves a mad scientist detonating a doomsday bomb. Meanwhile, Mrs. Frederic and the Regents try to determine what MacPherson left behind in Leena's mind.
Models turn up dead, aged into elderly women. To find out who is responsible, Myka goes undercover as a fashion model to find the killer... and becomes the next victim. Meanwhile, Claudia goes on a non-date with local hardware clerk Todd.
The Regents send Douglas Fargo, tech expert from Eureka's Global Dynamics, to upgrade the Warehouse 13 computer system. However, a 35-year-old backup computer activates, and the program decides that the warehouse's human staff are the primary threat to the building's integrity.
Mrs. Frederick secretly recruits Pete to find a mole within the organization who is buying artifacts. However, when the mole finds out, they go after those closest to Pete.
Claudia goes on her first full-fledged field mission to determine why wrestlers are spontaneously combusting. Meanwhile, H.G. Wells returns.
Pete and Myka inadvertently activate an artifact that causes them to swap bodies. However, they soon discover that the swap has fatal consequences. Meanwhile, Claudia accompanies Artie on a case involving a seduction artifact, and has to take over when Artie becomes an obsessed stalker.
Someone is using artifacts from Artie's past with the Russians to kill his allies in the present, and Helena is the prime suspect.
When ex-Warehouse agent Rebecca Sinclair brings them an unsolved case involved a newspaper editor who murdered his wife and three secretaries in 1961, Pete and Myka use H.G. Wells's time machine to travel back and try to determine what artifact was used. Meanwhile, Artie refuses to trust Helena, the newest Warehouse agent.
The deaths of three students in Egypt set off a chain of events that result in Mrs. Frederic's impending death, the appearance of a Regent, the revelation of the long-lost Warehouse 2, and the presence of a traitor within the team.
Helena's trail takes Pete and Myka from Paris to Wyoming, and they realize that she has obtained an artifact of vast destructive power... and plans to use it to destroy humanity. Meanwhile, Kelly encounters an artifact for the first time.
Pete and Myka are on the trail of a right jolly old elf who is haunting a businessman who has abandoned his family. Meanwhile, Claudia decides to give Artie the greatest Christmas gift ever and tracks down his estranged father, Isadore.
After Myka leaves the warehouse, Pete gets a new partner: ATF agent Steven Jinks, who has a gift for sensing when someone is lying. Pete and Steven take on a new case in Denver, while Artie, Claudia, and Leena deal with a deadly pair of statues at Warehouse 13.
While Pete and Myka go after someone using an artifact to induce Alzheimer's, Claudia goes on her first case as a full agent with Steve to track down Typhoid Mary's knife.
While Artie and Claudia meet with Vanessa Calder and Hugo Miller to investigate a computer virus that transforms people into clay, Myka and Pete wake up naked in bed and try to find a missing Steve.
While Claudia and Steve attempt to infiltrate a Civil War reenactment to recover U.S. Grant's flask, Pete and Myka must deal with Pete's ex-wife... who has been stung by an artifact bee that has turned her into a human queen bee.
When a series of mysterious disintegration deaths occur in Pittsburgh, the team discovers that the artifact responsible, Joshua's Horn, has ties to Helena's time as an agent in 1893.
Pete, Claudia, and Myka are called in to help Fargo, who is trapped in a virtual reality swords & sorcery game. Meanwhile, Artie and Steve are summoned to New York to recover an artifact... by FBI agent Sally Stukowski.
While in Denver, Myka picks up the trail of the counterfeiter who killed her former partner, Sam Martino. Meanwhile, Artie, Claudia, and Steve interrogate a dog that witnessed the theft of an artifact.
Sally Stukowski and her partner make their move, attacking the Regents and using an artifact to trap them in a building and bring it down around them.
While Pete and his mother Jane try to determine the origins of their mysterious opponents, Myka and Claudia travel to Portland to stop a girl who can apparently vaporize anyone she hates with blasts of radiation.
Myka and Pete deal with a plague of zombies in Ithaca, while Claudia deals with a new romance, a prophecy of death, and a rejection from a friend.
As Sykes begins his end game, the agents discover that Helena is still alive... and teaching high school literature. Meanwhile, Jane reveals the full extent of her plan but one agent will lose their life carrying it out.
As Christmas approaches, Pete inadvertently activates an artifact that sends him to a reality where he never existed. To thwart an old enemy, Pete must gather Myka, Artie, and Claudia from their new lives and return to the warehouse to undo the artifact's effects.
Season 4 kicks off with the Warehouse Team still reeling from the shocking events of the climactic season three finale – the loss of Agent Steve Jinks, Mrs. Frederic, H.G. Wells, and the destruction of the Warehouse itself. Their only hope lies in racing to the other side of the Earth to hunt down an obscure artifact, which may or may not even exist – and if it does exist, what consequences will they face for using it?