A few years ago, Kevin and Matthew McManus produced and wrote episodes for a brilliant little Netflix series called American Vandal. That show managed to playfully subvert expectations and defy genre conventions in a visually arresting way to create a complex and incredibly entertaining narrative. So it shouldn’t have surprised me that the brother writing/directing duo would continue to confound with their first foray into horror.

It begins with a rumbling noise. An indescribable sound that vibrates through your being like a wavelength but on a much grander scale. It sounds like it belongs to the belly of some monstrous creature. It sounds angry. It sounds demanding. It sounds hungry. The sound continues from a black screen to the sight of a lone fishing vessel in the inlet of Block Island, a real place off the coast of Rhode Island. In the boat lies an unconscious man named Tom (Neville Archambault) who gradually awakens, wide-eyed and fearful. His boat is filled with dead fish and a rope dangles overboard...but whatever was attached to the rope is long gone.

And that rumbling sound continues.

Tom’s adult son Harry (Chris Sheffield), meanwhile, throws a couple beers back with some Block Island locals at a bar. One of the patrons is named Dale (Jimm Cummings) and he spins wild conspiracy theories about the government using the Toxoplasmosis found in cat poop to control the population. As Harry drives Dale home, a bird splats into the windshield and Dale has a theory about the birds, as well. He talks about the thousands of birds that dropped from the sky in Arkansas and he might be incredibly interested in the nine or ten tons of fish that keep washing up on Block Island’s shore…

Harry’s sister Audrey (Michael McManus) certainly is. A marine biologist, the discovery has forced her to return to her home on Block Island to study the dead fish. Joined by her daughter Emily (Matilda Lawler) and her associate Paul (Ryan O’Flanagan), she returns home to discover her father in the grips of what appears to be dementia and a brother who seems unable or unwilling to see it. But when tragedy strikes, Harry is forced to confront not only the terror that’s gripping his small island but also the illness plaguing his father that has seemingly found its way into him.

The Block Island Sound is clever down to its punny little title. Obviously, the “sound” in question is the rumbling noise that not only plagues Tom but eventually torments Harry, as well. But it’s also a nautical term that describes the area between Block Island and the mainland. It’s a duality that benefits a film that likes to wade in different genres and defy expectations in the best of ways. The narrative is constantly reinventing itself, beginning as an ecological thriller that seems destined to be about some aquatic beast in the sound before transitioning into a paranoid thriller with hints of body horror. As if that’s not enough, when Audrey and Harry’s headstrong sister Jen (Heidi Neidermeyer) shows up, it’s also a family drama about a trio of siblings overcoming whatever trauma in their past split them up.

Regret and resentment have built up over the years so that when Audrey questions why Harry hasn’t done anything about their father, he responds that Tom’s just getting older: “You’d notice that if you came by more often.” Harry feels abandoned by his two sisters who made it off the island, leaving him to take care of their ailing father and the resentment sears off the screen. There’s also indication that Harry has anger issues and might be delusional as Audrey confides in Paul, “he gets paranoid. He refuses to believe the most obvious and simple answer is right.”

But is it?

Because like the conspiracy theories that Dale weaves, it’s hard to tell exactly what’s going on for the majority of the film. And yet it’s so tightly controlled that you have to just sit back and smile as the revelations are unspooled. It defies expectations and yet is told with such confidence and assurance. At least two startling revelations left me gaping and the turns they took and while the film generally shies away from special effects, two instances towards the end elicited a surprise gasp.

What makes it work, though, is the acting, particularly the relationships between Harry, Audrey and Emily. Even though Audrey describes her brother as kind of an asshole, it’s obvious Harry wants to be a better person and a good uncle to Emily and their connection is the core of the film’s thematic weight. But the script knows when to push on the horrific elements and when to just lay bare the fears gripping the small, crumbling family. It can go from a crushing moment when Harry collapses in a sobbing mess crying, “I don’t know what the fuck is happening to me,” to a moment of pure wonderment and surprise.

After the reveals and revelations were over and I went on to other festival films, I still found myself constantly thinking back to this movie. The Block Island Sound is as clever as its name would imply and left me with a giant smile on my face. It’s a genre-defying masterpiece and I recommend it full-heartedly.