Stephen Reinhart, an American scientist, travels to the remote town of Arkham to visit his fiancée, Susan Whitley. Upon arrival, he finds the townsfolk unwilling to assist him and is forced to walk to the Whitley estate. When he arrives, Susan’s father, Nahum Whitley, greets him with hostility and forbids him from entering certain parts of the house. Reinhart notices strange occurrences and unusual radiation around the estate but receives no explanations from Nahum or Susan's ailing mother, Letitia.

Reinhart’s curiosity leads him to investigate the strange energy seeping from a nearby greenhouse. Within, he discovers mutated plants and signs of an otherworldly influence. Susan confides in him about her father's secretive experiments with a mysterious meteorite that crashed near their home. As Reinhart digs deeper, he unravels the horrifying truth about Nahum's work and its monstrous consequences. The situation escalates as the dark forces created by Nahum's meddling begin to spiral out of control, threatening everyone at the estate.