In the aftermath of the warehouse's destruction, the Warehouse team races against the clock to find a way to undo time itself and put right what went wrong. However, Artie finds himself facing a difficult decision when he is warned that saving the warehouse will unleash an even greater evil.

While Claudia tries to help a friend and gets unexpected help, Pete and Myka investigate an artifact that causes crowds to see certain individuals as monsters... and attack them.

A cache of Walter Skyes' stolen artifacts turn up and all six agents go into the field to recover them. Artie unexpectedly reveals his secret to Leena, while Steve begins to realize the downside of the metronome that brought him back to life.

While Pete and Claudia help Hugo Miller track down a bag of marbles at a boy's academy, Myka and Steve travel to New Orleans on the trail of another artifact while Artie meets with Brother Adrian.

While Pete and Myka go to Toronto to investigate an invulnerable hockey player, Steve helps Artie track down stolen artifacts while Claudia meets with Mrs. Fredericks to discuss her future as a warehouse guardian.

The Brotherhood continues its assault on Artie's life, targeting someone close to him with Alice Liddell, the imprisoned spirit within the Dodgson Mirror. Meanwhile, Claudia learns of the connection between her and Steven.

While Pete and Myka travel to West Virginia to investigate a rust-like infection among steelworkers, Steven and Claudia go to Steven's home to find a way to break the metronome's hold on him. Meanwhile, Helena, Leena, and Mrs. Frederic confront Artie with their knowledge of what he has done.

Pete, Myka, and Claudia set off to rescue their loved ones when Brother Adrian sends them deadly artifacts. Meanwhile, Mrs. Frederic and Steve travel to Rome and learn Adrian's dark secret.

The team have no time to mourn a fallen comrade as they go after the person responsible, the nemesis that has been stalking Artie since he used Magellan's Astrolabe to save the world.

With the fate of the world in their hands, Pete and Myka's only hope of finding a cure to the Sweating Sickness is a drunken history professor. Meanwhile, Steven and Claudia enter Artie's subconscious in an attempt to bring him out of his coma before he fades away for good.

While Pete and Claudia travel to Oregon to look for an artifact used to kill enemies of the environmental movement, Artie deals with the repercussions of Leena's death.

A mishap with an artifact traps Pete and Myka in a fictional 1940s world where they have to solve a murder to escape... but someone doesn't want them to. Meanwhile, Claudia and Steven convince Artie to go along with them to investigate reports of stolen cars, and Artie starts taking dangerous risks.

While Pete and Myka travel to Las Vegas to investigate two deaths where the people inexplicably fell from great heights, Claudia and Steven investigate two jockeys in London who went into comas after winning their races. Meanwhile, Artie gets a visitor to the warehouse.

H.G. has created a new life for herself in Wisconsin, but calls in the agents when she comes up against an unidentified artifact. Meanwhile, Abigail joins the others on the floor of the warehouse to track down the source of mysterious tremors that threaten to destroy the building.

Pete, Myka, and Steven team up with a U.S. Marshal to track down two prisoners who used a lava-spewing artifact to escape prison. However, they discover that the Marshal is Steve's ex. Meanwhile, Artie and Claudia try to track down part of an artifact that is rendering Artie deaf...

Someone in a gated community is using an artifact to extract vengeance and Myka and Pete go to investigate. Meanwhile, Artie and Claudia help a teen suffering from dangerous visions, and Steven and Abigail clean up the warehouse.

The agents track down a cache of artifacts stolen from Warehouse 12 by the infamous Roaring Dan Seavey... and guarded by his ghost. Meanwhile, Charlotte Dupres makes her move with the help of her inside person.

Pete, Myka, and Charlotte must track down Sutton, the only man who knows where they can find Paracelsus and exchange the Philosopher's Stone for the stele that will free Claudia from her bronze imprisonment... before she disintegrates.

Pete and Myka capture Paracelsus but not before he makes himself immortal. When Myka's cancer becomes worse, Pete must make a deal with Paracelsus to cure his partner. Meanwhile, Claudia receives some startling news from Artie.