Gjunheim was a Deathwatch Sergeant stationed on the Watch Fortress Haltmoat, when it began receiving numerous reports of ships disappearing near the Tiamet System. In order to determine what had happened to the ships, Watch Commander Vilnus sent Gjunheim and his Kill-Team to survey the System held by Hive Fleet Tiamet. The Kill-Team is able to infiltrate the System and land upon the Jungle World Ziaphoria, where they discover a continent-spanning organic conical structure. When they near it however, the structure pulses and sends out a tsunami of psychic energy that rolls across the world. This overwhelmed the defenses of the Kill-Team's Librarian and causes his head to explode, which alerts the Hive Fleet to their presence. As the Tyranids close in on them, Gjunheim manages to send one final vox transmission to the Kill-Team's orbiting Corvus Blackstar, warning of the nightmare they have uncovered, before the Space Marines are killed by the Xenos. The Corvus is able to reach their ship, which then escapes from the Tiamet System and returns to Watch Fortress Haltmoat with Gjunheim's message.