The evil Eve Baird as a member of DOSA
Eve Baird (Rebecca Romijn) is a hidden (redeemed) villainess from TNT's The Librarians. She is a former anti-terror agent for NATO, and in the pilot episode, "And the Crown of King Arthur," she becomes the Library's new Guardian; tasked with training fellow Librarians Jacob Stone, Cassandra Cillian, and Ezekiel Jones. As the series progressed, Eve developed a close partnership with veteran Librarian Flynn Carsen, which became romantic by the second season.
In Season Three's penultimate episode, "And the Fatal Separation," it is revealed that Eve is actually a sleeper agent infiltrated by the Department of Statistical Anomalies, a villainous agency who had been pursuing the Librarians. The revelation came during Eve's encounter with General Cynthia Rockwell, the evil leader of the DOSA, who made the revelation regarding Eve's role--an unwitting role. Eve was used by DOSA to gain access to the Library, with Cynthia claiming that they were a terrorist organization due to their connection to magical artifacts. She was later rescued by Ezekiel, and she reunited with the Librarians as they witnessed Charlene's separation from the Library. The episode ended with Eve at the Chamber of Memories, which stored candles that represented souls of people linked to the library. Eve watched as Charlene's flame was extinguished, doing so with an evil smirk, hinting a possible heel turn.
Eve turned heel in the season finale, "And the Wrath of Chaos," when she aligned with DOSA and allowed them access to the Library. As part of her villainous ruse, the evil Eve sent the three Librarians to Mount Rushmore on a case involving a mystical dreamcatcher, which was a diversion that would leave the Library vulnerable. Eve, now in a DOSA uniform, led the group into the Library, and even handed Cynthia a bust of Medusa's head to turn Jenkins into stone. Jacob, Ezekiel, and Cassandra returned from Mount Rushmore and witnessed DOSA's infiltration of the Library, while also learning about Eve's heel persona and alliance with the group. However, when Eve was confronted by Jenkins and the Librarians, she revealed that her role was part of her and Flynn's larger plan to trap and vanquish Apep, the Egyptian god of chaos, which they and the Librarians accomplish with the Eye of Ra. As a result of this, Eve was redeemed and remains with the Library.