Eventually, Valkris became one of the few females to lead a Klingon Great House, having been chosen for the honor over Kiosan. The shame of this drove Kiosan to dishonorable behavior. Kiosan's dishonor had tainted the House so badly that Valkris was forced to disown him. During this time, she became involved with Commander Kruge, feeling that he would help her regain some of the honor she lost due to Kiosan's actions. For his part, Kruge admired the young woman as a fierce warrior.
After the Klingon Empire became aware of the existence of Project Genesis, Valkris undertook a mission to obtain a copy of the Project Genesis data. She was able to obtain a report filed by then Admiral James T. Kirk, who had included a summary of the Genesis Project data. Once she had seen the data for herself, Valkris obtained transport on board the freighter Merchantman, which rendezvoused with Kruge's Bird-of-Prey. Valkris transmitted the data to Kruge, telling him that he would find the data useful.
Kruge realized that Valkris had seen the data. Telling her that it was unfortunate, Kruge proceeded to attack and destroy the Merchantman, killing Valkris as well as most of the Merchantman's crew. (TOS movie & novelization: Star Trek III: The Search for Spock)