Pete and Myka return to Washington to intercept a samurai sword that is to be presented to the president, and they discover a competitor for items that belong to the warehouse.

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.

As the Warehouse team prepares to celebrate the holidays in snowy South Dakota, Pete and Myka are called upon to hunt down a malevolent Santa Claus. Meanwhile, in time for Hanukkah, Artie and his estranged father, Isadore Weisfelt reunite after 30 years.

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.

While Pete and Myka investigate a series of artifact-related growth spurts, Artie reluctantly takes Steve and Claudia with him to track down Brother Adrian before he can steal more artifacts from 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.

While Pete and Myka team up with two former Secret Service co-workers to investigate a series of bizarre deaths in Washington DC, Artie agrees to show Claudia how and why her sister had to disappear.