Stephen King’s work, highly informed and influenced by sf traditions of the 1950s and 1960s, often fuses these sensibilities with the genre for which he has become known, horror. This has resulted in a very specific genre hybrid that King has used in two novels adapted for film and television, which I call the alien possession tale. In these stories, humans become subject to the influences of extra-terrestrial consciousnesses, blending the sf alien invasion subgenre with the horror possession subgenre. The Tommyknockers (1988) and Dreamcatcher (2001) blend these two subgenres into distinct hybrid stories. While the novels very clearly highlight both the aesthetics and the inherent fears embedded in the sf narratives from the 1950s and 1960s, the adaptations – The Tommyknockers as television miniseries (US 1993) and Dreamcatcher as a feature film (Kasdan US 2003) – tend to capitalise and focus upon the elements of the genre in which King is known as a master: horror. This article addresses this genre hybridity and the shifting genre emphasis between original narrative and adaptation. It looks at the horror tendencies within the adaptations, which mute sf elements, and King’s straight possession tale Desperation (novel 1996; television miniseries US 2006) to show similarities in depiction. This is done to demonstrate the tension between stories developed by King and adaptations marketed towards audiences familiar with him as a horror writer.