This was a new twist on the frankenstein story. His creator started with a body and then looked for a brain. Herb Evers, having crashed the car and decapitated his girlfriend, keeps her head alive presumably to have someone to talk to on those long winter evenings?
She, however, prefers to talk to some unspeakable monster who inhabits the locked cupboard across the room. While poor boyfriend is out looking for a body for his true love, she's doing mind games with horror boy. It can only end in tears, although in this case 'flames' might be more correct.
An oldie but still worth a look, and a worthy edition to your old horror film collection!