A wealthy but dying industrialist hires a team to investigate the notorious Belasco House, reputed to be the "Mount Everest of haunted houses." The team is composed of physicist Dr. Lionel Barrett, his wife Ann, mental medium Florence Tanner, and physical medium Ben Fischer, the latter being the only survivor of a previous investigation. As they enter the house, they are immediately confronted by a series of paranormal phenomena, with Florence and Fischer experiencing strong supernatural presences. Dr. Barrett remains skeptical and is determined to prove that these events can be scientifically explained.

As the investigation proceeds, tensions escalate among the group as they encounter increasingly dangerous and bizarre occurrences. Dr. Barrett uses sophisticated equipment to examine the house's many mysteries, while Florence attempts to communicate with the spirits she believes are imprisoned there. Fischer, wary from his past experience, is reluctant to participate fully but feels compelled to help uncover the truth. The house’s dark history begins to unravel, revealing layers of malevolence and tragic past events. The team faces not only the house’s powerful forces but also their internal conflicts, testing their resolve and understanding of the supernatural as they strive to unlock the secrets hidden within its walls.