The new genre-bending film The Lighthouse is hard to describe. I’ve seen it mentioned as everything from a horror film to a dark comedy to a psychological thriller. I can’t really tell you what it is, but I can tell you what it’s about, and why you should see it.

The basics are pretty straightforward: Set in the 1800s (and probably Nova Scotia), Willem Dafoe (who’s known as an often-outstanding actor) and Robert Pattinson (who’s not) pair off as lighthouse keeper Thomas Wake and his drifter-turned-apprentice Winslow, respectively. Winslow, due to circumstances he eventually and somewhat grudgingly reveals, has signed on for a month stint alone with Wake on a tiny isolated, storm-swept island. Dafoe’s Wake is a bearded, crusty tempest, with flashing eyes and a thick brogue. Pattinson, gaunt and haunted, resembles a young Powers Boothe under a bristly black mustache.

Dafoe’s Wake is alternately sadistic, inscrutable, arguably mad, and a sad, lost soul. He has no tolerance for the teetotaling Winslow, who seems determined to work hard and follow the rules, at least long enough to earn his pay and get off the damned sea-drenched rock. Winslow is trapped (well, they both are) at least until the next monthly supply boat comes—assuming it can make it through the storm. As the story goes on we come to know more about the men, and hints of secrets each may be hiding. The claustrophobic cinematography contributes to the sense of desperation and dread.

The choice to film in black and white can come off as showy (Sin City, for example) or understated (Pi, for example), but works well in The Lighthouse. The film is as stark as the characters, and everything is extreme. The light that the lighthouse projects of course must be powerful enough to be seen for miles and is blinding up close. The foghorn as well must be heard at great distances, but is deafening nearby. Everything on the rocky clot is dangerous, or at least unpleasant, and nothing is easy.

The Lighthouse reminded me of other films which involve a psychological struggle of wills between two characters, such as Jane Campion’s Holy Smoke (1999, about a cult deprogrammer and his ward) and William Friedkin’s Bug (2006, about a drifter and the lonely woman he meets in the California desert). Films like these require strong performances, and both Dafoe and Pattinson deliver.

The Lighthouse is laden with symbolism—in fact perhaps a little too much of it—with folklore and legend helping give the script its power. The film has touches of Lovecraft and Poe (with a seagull instead of a raven as an avian portent of doom), and many threats to sanity lurk in the shadows cast by the lighthouse. Isolation is one; liquor is another. Winslow starts to have visions horrific and alluring, and sometimes both at the same time. He glimpses what he thinks is a mermaid, and comes to suspect that a seagull has it in for him (he’s probably right).

The lighthouse itself is a character, and director Robert Eggers gives it its due. We see its inner workings—the levers and chains and pulleys and coal-fired furnaces—though not necessarily its secrets. There are lighthouse fanatics, just as there are train fanatics and covered bridge fanatics, and I can see why: they’re symbolic and archaic. The film’s thunderous soundtrack works too hard to drive home the story’s beats, and could have been profitably dropped by a dozen or so decibels. If The Lighthouse suffers a bit from a murky plot, the haunting atmosphere and acting more than make up for it.