The newly assembled Librarians investigate a mysterious dancing sickness, leading them to a showdown with a powerful magical factioneer at a professional ballet company.
Charlie, Lysa and Connor find themselves in a strange manor with ongoing Christie-style murders. As they work to solve the mystery, Vikram searches for them with help from a tarot reader.
After a bachelorette party with Lysa's best friend from childhood, the team wakes up in rough shape and with horrible hangovers. They also have no idea how they ended up where they are.
When Vikram attempts to return to 1847 via a homemade time machine, he inadvertently transports the entire team back to the days of King Arthur, where they learn the truth about a Knight of the Round Table, Camelot, and Elaine.
When graffiti starts coming to life and threatening a teenage girl, the team have to work out how these strange events are related to Gregor's Hammer -- and the imminent return of Gregor himself.
General Gregor retrieves the Sword of Mars and uses it to take over the country of Caucasylvia (remember from the Train episode), gaining control of their nuclear arsenal. The team must steal the Sword to prevent world calamity.