Penny makes it to the Underworld and after faking some Game of Thrones spoilers, is led to Benedict. Unfortunately, the mapmaker doesn’t have the key, but he knows who does: The Librarians. Swerving Benedict, Penny makes his way towards The Library, where he runs into Victoria.

Over her untimely death, she reveals that she knows Penny’s plans--through "his book"--and takes him to the person who writes everyone’s futures. Freakily, it’s an Alice clone. There Penny lives out most of the episode, reading what is happening to his friends. It's through those pages he is able to locate the fifth key, going back to The Library to send it and gim off.  Unfortunately, Victoria simply hands him over to The Library.

Back at Brakebills, Irene stops by to get that favor from Julia, and a recently appeared Fen sees Irene’s companion: a slave fairy. The discovery takes Fen and Julia on a mission to talk with this slave fairy, Sky, but when they find her, her leg has been chopped off. It’s revealed that Sky’s leg was used to create that potent magical powder Julia snorted.

Meanwhile, Kady, Harriet, Poppy, Quentin, and Olivia attempt to make a mirror bridge to get them into The Library. Alice discovers this, revealing the danger without the necessary magic (and mathematics). Alice is unwilling to help, so Poppy steals some of her notes to get the group on their way. They all make it into the Library and struggle to find the key Penny was supposed to drop off.

As Poppy, Quentin, Kady and Harriet dash around the library, they each run into their own issues--including Alice, a very large dragon and Zelda. In the process, it becomes clear Alice is looking for a way back to finishing her plans as a niffin, Poppy isn’t interested in risking her life, Quentin is growing farther from Alice, Kady loses Penny, and Harriet’s antagonistic relationship to the Library is rooted in her familial relationship to Zelda.