A young couple, Sally and Alex Farnham, inherit a large, gothic mansion from Sally's recently deceased grandmother. Eager to make the place their own, they begin renovations, with Sally particularly interested in converting the mysteriously sealed-up fireplace in the basement into a den. Despite the warnings of the aging caretaker, Mr. Harris, who insists that the fireplace should remain closed, Sally's curiosity gets the better of her, and she ultimately manages to open it, unknowingly releasing creatures that have been trapped inside.

The small, whispering creatures quickly become an unsettling presence in the Farnham's home, mostly perceptible to Sally. She becomes increasingly distraught by their mysterious appearances and strange noises, which seem intent on luring her into the dark and shadowy corners of the mansion. Her husband Alex, preoccupied with his work and skeptical of the supernatural, dismisses her concerns, attributing her anxiety to stress and isolation. As the creatures become bolder, Sally's sense of reality begins to unravel, leaving her to struggle with convincing Alex and the caretaker that the threat lurking in their home is real and malevolent.