Willie's parents went on sabbatical in 2367, and by special arrangement, allowed their children to remain aboard the Enterprise-D with the stipulation that they both stay out of trouble. The starship stopped over at Ogus II that year, and Jake and Willie visited the planet's laser duel games. Jake tricked Willie into believing that he had killed Jake by breaking a balloon filled with red pillion dye after Willie fired the laser pistol at him. Frightened, Willie fled into a forest. While there, he ingested a cove palm fruit and was infected by the deadly parasites inhabiting that fruit. Although he was immediately placed into quarantine and cared for by Doctor Beverly Crusher, the advanced facilities of Starbase 416 were needed to fully eliminate the parasites.
The Enterprise-D rushed to the starbase, but was temporarily diverted after Lieutenant Commander Data hijacked the ship and took it to the Terlina system after receiving a signal from his creator, Noonian Soong. The lost time caused Willie's condition to deteriorate, but control of the ship was restored and Willie was brought to the starbase in time.
Willie felt some anger towards Jake, which caused Jake to feel even more guilty over causing his brother's condition. However, the two were able to make amends and played together once Willie received treatment. (TNG: "Brothers")