In the mirror universe, Selar was a female Vulcan member of Memory Omega, working against the Klingon-Cardassian Alliance undercover in the Terran Rebellion and aboard Captain M'k'n'zy of Calhoun's starship Excalibur. She was a scientist by training, but also an excellent combat medic. (ST - Mirror Universe novel: Rise Like Lions; TNG - Mirror Universe novel: The Worst of Both Worlds; NF - Mirror Universe short story: "Homecoming")
Sometime after 28 September 2371, Selar was part of a three-person team investigating unconfirmed reports that the Alliance was developing metagenic weapons underground on Celtris III. The other team members were team leader Vash and explosives expert Bagro, a Tellarite who had created a bomb to destroy any weapons they found.
The team found one Cardassian soldier guarding a steel hatch, beyond which the metagenic signature was emanating. Selar felled him with a Vulcan nerve pinch and then suggested using a Ceti eel to ensure that he gave them the correct code to open the door. Selar, who was carrying an eel in a vial in her pouch and admitted to having "sources" to obtain the outlawed mollusks, considered employing them to be "distasteful"; however, she thought it would be worse to allow the Alliance to freely develop metagenic weapons, which were banned by treaty with the Romulan Republic. Selar applied the eel to the soldier, obtained the door code and then killed him mercifully using Tal-Shaya.
The room beyond, however, was empty, save for a device emitting a false metagenic signature. Vash used Bagro's bomb to blow open the steel hatch and allow her team to escape, but Selar was wounded in the leg by a disruptor beam from an Alliance strike force. Bagro carried her over his shoulder during their flight until, eventually, he was stunned into unconsciousness. Selar told Vash to kill her and Bagro to prevent them from falling into Alliance hands for interrogation, but Vash refused. Selar attempted to reach her disruptor to do the job herself, but she was stunned unconscious by the Alliance strike force.
Vash escaped on her own. Bagro survived and endured horrific torture at the hands of Cardassian Gul Madred. Selar was said to have "taken her own life" while jailed. However, this was not the end of her story. (TNG - Mirror Universe novel: The Worst of Both Worlds)
In the late 2370s, Selar, disguised as a Romulan named Thue, was in an emergency life capsule when she was rescued by the Excalibur, a Thallonian-built starship. She claimed that her transport ship, which was making a cargo run to Romulus, was attacked by Alliance forces. They boarded the vessel and killed the crew. Their interest was only in the cargo, which was intended to create a weapon.
"Thue" suggested that it would be wise for Captain Calhoun and his crew to make an ally of Praetor Hiren, rather than allowing the Alliance and the Romulan Republic to destroy one another. She said the Excaliburs' recent defense of colony worlds had not gone unnoticed by her, the Romulans, or the Alliance. She predicted that the Alliance would eventually target Excalibur for destruction. For that reason, "Thue" said told Calhoun he should throw in his lot with Hiren, whose empire stood a chance of defending itself against the Alliance.
Soleta, who opposed any alliance with the Romulans, later broke into "Thue"'s assigned quarters while she was sleeping in order to find out what she was hiding. While using her ability to probe "Thue"'s mind, she encountered resistance and before she was forced to break the link, she discovered Selar's identity as a Vulcan.
Selar claimed to be merely spying on the Alliance, since there was no love lost between her people and the oppressive regime. However, when the subject of the women's ability to use the Vulcan mind meld came up, Selar swore Soleta to secrecy, claiming the future of all Vulcans was at stake. If the Alliance ever discovered this ability, then all Vulcans might be "rounded up, experimented on, or perhaps simply annihilated outright because of the threat we would present". In exchange for Soleta's silence, Selar revealed her true identity to Calhoun and the crew.
Later, when the Excalibur overtook and boarded the transport ship from which Selar originally had come, the Vulcan identified its cargo as C-170, a radioactive isotope used in the construction of weapons involving Thalaron radiation. C-170 would generate a cascading biogenic pulse sufficient to destroy a planet. Selar theorized that the Romulans already had the rest of the materials necessary to complete a Thalaron bomb. In order to infiltrate Romulus and enlist Hiren's aid, Selar agreed to disguise Calhoun as a Romulan.
Selar believed that the Alliance had left the Romulan Republic relatively unmolested because it was awaiting the creation of the Thalaron bomb. When she met Hiren, she learned that he had, in fact, long been promising this to the Alliance. However, when the bomb was finally assembled, Cardassian agent Tome Ari announced that it would be tested on Romulus.
In the ensuing conflict between the Romulan and Alliance forces, the Thalaron bomb fell into Tome Ari's possession and Selar was unable to grab it before he set it off. The Excalibur beamed up Calhoun, Soleta, Selar and Hiren, but the surface of Romulus was rendered uninhabitable for 950 years. (NF - Mirror Universe short story: "Homecoming")
Selar used a master quantum transceiver to contact Colonel Keiko Ishikawa on behalf of Calhoun, who wanted to join General Miles O'Brien's Terran Rebellion. After the rebel leaders' disastrous first meeting, however, Selar reported to Memory Omega's Director Saavik that the men's egos were incompatible. She recommended that the secret organization recruit an outside leader who both rebel factions would accept and follow in an offensive against the Alliance. Selar said that leader could not be Calhoun because his ruthlessness and brutality were incompatible with Memory Omega's philosophy. When Saavik asked if Selar could manipulate Calhoun telepathically, Selar said no because of Calhoun's psionic connection with the much more powerful Mark McHenry.
Two days later, Selar revealed the existence of Memory Omega to O'Brien and Calhoun, and also that the organization had chosen Captain Jean-Luc Picard of the free starship Enterprise to lead the two rebel groups against the Alliance.
In 2378, Selar narrowly avoided death when McHenry transported her and the entire Excalibur crew into Hangar Bay One of the Enterprise. McHenry then collided Excalibur with a Klingon bird-of-prey carrying a trilithium warhead that was intended to destroy Bajor's star, B'hava'el. (ST - Mirror Universe novel: Rise Like Lions)
- No explanation was given in the "Mirror Universe" novels for Selar's apparent death on Celtris III and later reappearance. However, given her involvement with Memory Omega, it may be presumed that she was covertly rescued, possibly via subspace transporter, before she could be interrogated.