Night of Evil by Genevieve St. John [1967]

Excellent. :-) It's a 5 on a scale of 1 - 5.

This novella (it is 81 pages long but packs all the entertaining punch of a regular full-length novel) is one of Belmont's "Double Gothics":

http://www.fantasticfiction.co.uk/s/genevieve-st.-john/castle-of-closing-doors-night-of-evil.htm

The story concerns Judith Porter, a 23 year old woman who leaves her father's home in New York City to attend her ailing Aunt Carol at Bay House, on Chesapeake Bay. Judith dislikes Bay House, the intensely foggy days and the eerie wails of distant foghorns.

Judith is taking a tray up to her Aunt Carol, is midway up the tall staircase when she becomes mesmerized by fog drifting into the room below. How can this be? The doors and windows are securely shut, the casements are tight. Judith's hands weaken and she drops the tray upon seeing the fog thickening...seeming to become upright...taking on a human form. She huddles onto the staircase, screaming; when she dares to look again, the menacing foggy form is gone.

This is just one of many seeming hallucinations -- both visual and auditory -- Judith has been suffering from since arriving at Bay House. She seeks a rational explanation, but is plagued with fears of insanity. The author pulls some very unique and clever tricks out of her hat in the tormenting of our fictional heroine.

Also residing in Bay House are Gregory Stanton, a questionable character whose presence Judith questions and who is entirely devoted to Carol; Dr. Craig Wilson, Carol's young private physician on whom Judith has a crush; Miss May Millner, the "difficult" housekeeper and cook, and Tom Bradford the maintenance man. Mr. Arthur Porter, Carol's father and Judith's grandfather, returns from his rest home in Baltimore for a weekend stay at Bay House. Judith is puzzled as to why her wealthy old grandfather chooses a nursing home two hours away, when he could be privately cared for in the luxury of his grand estate.

Judith tries to solve the perplexing mysteries around her. But the biggest mystery of all is whether she's the victim of cruel hoaxes and pranks...or if she's rapidly losing her mind, as her mother -- who committed suicide when Judith was 12 -- did.

My only (admittedly petty) criticism of the story is that Judith seems perhaps 18, not a more mature 23. She's a terrific character, but a mite bit immature for 23 [especially in 1967].

It reads neatly, swiftly; stays on track. It was a short and wonderful "interim" read while I'm awaiting the replacement for the previous novel I'd started, with the 15 (or so) missing pages.

I'm unsure if this novella is available separately or only appeared in "Double Gothic" form with Ms. Winston's story.

The cast of characters as I visualized them:

Judith Porter: Sally Field [age 23]
Carol Porter: Marie Wallace [age 44]
Mr. Arthur Porter: I can't recall the actor's name nor credits, but recall the face.
Gregory Stanton: Jerry Lacy [age 40]
Dr. Craig Porter: Warren Beatty [age 25]
Miss May Millner: Maggie Smith [age 61]

The cover art: A somber blue-gray background; young woman to the left, with flowing blonde hair dressed in an ankle-length and full-sleeved reddish dress; three black dogs chasing her across tall green grass; to the right a two-story shadowy manse in the background with a turret and one [of course!] lit window.