Visually memorable but somewhat demanding, “A Ghost Story” takes the simplest Halloween costume — a white sheet with eyeholes — and creates a touching story of loss and grief.

Casey Affleck and Rooney Mara star as a young couple torn apart when he dies in a car accident and lingers as a ghost — wearing an actual white sheet, complete with droopy black eyes, over his head and body. The simplicity of the image allows the depth of the film’s emotions to shine.

Whatever whimsy this costume and conceit suggests is tempered by a very somber and sometimes excessively slow pace. I’ll go ahead and admit that I dozed off (briefly!) during the scene when Mara eats an entire pie a friend brought her, but I kept waking up, and she was still eating the pie.

I do like Mara as an actress, but she is almost as expressionless as the guy with the sheet over his head. The always-sulky Mara seems to be in a state of stylish mourning in all her movie roles, so she is a natural here, but a bit more dialogue might have kept my eyelids open more easily.

But once you get past the pie scene and experience the film as a whole, it really is quite moving. The widow sells their house and moves away, but the husband’s ghost remains. Eventually, we learn of his attachment — to his wife, of course, but also to the house itself.

The scenes of their married life are a welcome center to the film, giving us a more realistic grounding that enlivens the wordless, faceless ghost. (I’m also very curious to know if Affleck came to the set and stood under that sheet every day.)

The ghost sheet costume is more beautiful than it sounds, and exceeds the Charlie Brown costume you might imagine; it is quite graceful and, well, haunting. His trek from the morgue, across a wide plain to his modest, beloved little ranch home is marvelous. The frustrated, angry ghost proves periodically menacing, and genuinely, intentionally frightens the house’s subsequent occupants.

He tries in vain to pull a tiny note his wife left from a painted-over crack in a doorway. There is more to this film than just artsy standing around. But there is also a lot of artsy standing around.

Without giving away too much of the plot, I’ll tell you that as time marches on for the housebound ghost, his surroundings change, and there are some beautiful, memorable scenes here. An event causes a major time shift, and themes of eternal recurrence are given a really nifty and satisfying treatment. Just when it is needed most, we get a beautiful and meaningful conclusion.

“A Ghost Story” is a short film that becomes more abstract and fable-like as it goes on, and its tight runtime suits it, four-minute real-time pie consumption notwithstanding. For all its potential pretension, it has a true emotional core, but I will admit that it took awhile to get there. However, taken as a whole, this film is a bit magical, romantic and profound, and the end justifies some of the earlier scenes.

Hang in there, and “A Ghost Story” has rewards. Maybe plan your own pie snack to get you through some of those dialogue-free slogs.

“A Ghost Story” is currently available to rent.