The fourth season does away with season-long story arcs in favor of stand-alone episodes, with three ongoing issues: Before the vernal equinox, Flynn and Eve must undertake a ceremony that will bind them to each other and to the Library, as Charlene and Judson did before them. They will become immortal and bind the Library to Earth, giving it a human connection and a human heart rather than the cold, implacable and dangerously self-centered attitude that would characterize it without that bond. (We learn in season three that the Library is a conscious entity.) The return of Nicole Noone, Flynn's first Guardian, believed dead and now immortal, raises many questions. And conflict arises between the Librarians over former Librarian Darrington Dare's assertion that there can only be one Librarian at a time, or the result will be disastrous. These three stories are not resolved until the last episode.
