《探險奇兵》第三季將堂堂出任務！隨著守護員Eve Baird以及Ezekiel, Cassandra 與 Jacob受命到圖書館成為圖書館員，卻沒有出現接受面試。圖書館員Flynn Carsen隨後出場，尋找圖書館(已失蹤在時空交錯中)，四個成為新的圖書館成員，目的在解決看似不可能的神祕謎題，保衛具魔力的工藝品，並攜手打擊超自然的威脅能量。
The Librarians are back for the THIRD SEASON! Follow Eve Baird, the Guardian, as well as Ezekiel, Cassandra and Jacob, who were asked to apply to the Library to become The Librarian, but didn't show up to the "auditions". And The Librarian Flynn Carsen. While Flynn is searching for the Library (which is lost in time and space), the four become a new team of Librarians in order to solve impossible mysteries, recover powerful artifacts, and fight against supernatural threats.