Magic exists but most people don't know about it. The artifacts that can cause mayhem are collected and stored in the Library, a magical place under the Metropolitan Museum of Art. The person who risks life and limb tasked with saving humanity from those that would use magic for evil is the Librarian.
The current Librarian is Flynn Carson and he's been on a lucky streak for 11 years. He needs a guardian and it seems chance has brought him to Lt. Colonel Baird. Baird is tasked with collecting WMDs for a special NATO task force when she runs into Flynn as he collects yet another artifact while helping her diffuse a bomb.
Baird is brought into the Library, invited by the Library itself, to become Flynn's new guardian. Someone is out killing previous candidates for Librarians, Baird and Flynn head to save three that were not on the list: Cassandra Killian, Jacob Stone and Ezekiel Jones.
Brought into the library, the new team faces odds they never fathoms with Baird trained the new Librarians as they work to save the Library and face down the Serpent Brotherhood.
All their quests, everything they do leads them to a final face off with stopping a total rewrite of history and ending the Brotherhood forever.