The younger sister of Kiosan, Valkris was chosen to lead one of the great houses of the Empire over her brother. Kiosan did not take the news very well, and behaved so dishonorably that it brought shame to the entire family. Valkris was forced to kick her older brother out of the family as a result. Valkris became involved with Commander Kruge, seeing him as a way to regain her lost honor.
Undertaking a spy mission, Valkris was able to get her hands on a copy of a report made by Admiral James T. Kirk on the Genesis Device. Viewing the report for herself, she arranged for a freighter to take her to a point near the Klingon-Federation neutral zone and hailed Kruge.
Kruge has his crew uncloak his ship, and Valkris began transmitting the data over to Kruge. When she remarked that Kruge should find the data useful, Kruge realized that she might have seen the data. Confirming that she had in fact viewed the data, Kruge decided to kill Valkris to keep news about the mission from getting out. He informed her of his decision by saying her viewing the data was unfortunate, to which Valkris replied that she understood.
On the Bird of Prey Kruge had his crew engage thrusters, swinging the larger Klingon ship away from the freighter. Nervous about the situation, the freighter Captain asked what was going on and when he would get paid off. Valkris responded that it would be very soon. As Kruge's ship came into position, Kruge remarked that Valkris would be remembered with honor before ordering his men to open fire on the freighter.
The freighter was quickly destroyed by the more powerful Klingon ship, killing Valkris in the process. In the novel Kruge had his men continue firing at the wreckage to ensure as much of it as possible was vaporized. Despite all that some of the crew survived and were able to warn Starfleet.
The assassination of Valkris by Kruge was director Leonard Nimoy's way of presenting to the audience the Klingon race's brutal mentality.