Valeris was a Vulcan protegee of Spock who served aboard the Enterprise in 2293 and was secretly part of the conspiracy to sabotage peace with the Klingons.
Valeris was the first Vulcan to graduate at the top of her class at Starfleet Academy, and Spock sponsored her career. She joined the Enterprise as helm officer for its final mission in 2293, escorting Chancellor Gorkon to peace talks.
Unknown to her mentor, Valeris belonged to a group of Starfleet, Klingon and Romulan conspirators who opposed peace. She helped make it look as if the Enterprise had fired on Gorkon's ship and later killed the two crewmen who had carried out the assassination so they could not talk. Spock set a trap that exposed her, and when she refused to name her fellow plotters, he performed a forced mind meld to learn their identities. This led the crew to Khitomer in time to stop a second assassination.
Valeris is a rare example of a Vulcan traitor in Starfleet, and her betrayal deeply affected Spock, who had believed that she shared his hopes for the future.