Dr. Edward Pretorius and his assistant, Crawford Tillinghast, have developed the Resonator, a machine intended to stimulate the pineal gland and expand human perception. Their experiment goes awry when they activate the device and it reveals an alternate dimension that exists parallel to our own. This discovery is not without consequence, as the machine also makes them aware of strange and malevolent creatures that exist within this other dimension. When an entity from beyond attacks, the incident leads to Pretorius' apparent death and leaves Tillinghast in a state of shock, accused of his murder.

The aftermath of the experiment catches the attention of Dr. Katherine McMichaels, a psychiatrist who takes an interest in Tillinghast's case. Convinced of the potential scientific importance of the Resonator and Tillinghast’s innocence, she arranges for him to be released into her care to recreate the experiment and document the effects under controlled conditions. They return to the Pretorius residence, accompanied by Bubba Brownlee, a police officer assigned to provide security. As they resume the experiment, they are unprepared for the horrific consequences as the machine not only unlocks the senses but also unlocks a gateway to a world of unspeakable horror that begins to infiltrate and distort reality.