The Countdown Clock is activated once the anchor chain to the Library is cut, causing the Library to disconnect from our dimension and have no entrance. Once the clock is activated, the Library folds in on itself before completely disconnecting from our dimension, leaving no way into it. The Countdown Clock has been activated at least once by Charlene and Judson in "And the Crown of King Arthur" to protect the artifacts within the Library from the invading Serpent Brotherhood. However, the Librarian can still access books from within the Library through Annexes around the world.