Kai Zook resided in Hanna City on the planet Chandrila alongside her two sons and her husband, Omar Zook, who served as an Imperial Corrections Officer. Her husband was assigned to the Imperial prison barge known as the Purge when the passengers aboard contracted a mysterious plague. After nearly all of the ship's occupants succumbed to the illness, and he himself became infected, Omar penned a letter to Kai. In it, he conveyed his sorrow for his absence in their sons' lives and affirmed his love for his entire family. Zahara Cody, the chief medical officer aboard the Purge, managed to retrieve this letter during her escape from the prison barge with Han Solo, Chewbacca, and Trig Longo, ensuring its delivery. Zahara and Trig ultimately succeeded in delivering the letter to Kai Zook, simultaneously informing her of her husband's death. Subsequently, the letter was made available to the public for scholarly examination pertaining to the Purge incident.