Austin Abrams as Jay Gardiner in a sticky situation in Whalefall

Jennifer Clasen/20th Century Studios

I’ll cut to the chase: Whalefall, a film about a diver who gets swallowed by a sperm whale and has only an hour to escape, is fantastic when it focuses on that very scenario. But every scene not set in a cetacean – and there are a surprising number – is an utter chore to sit through.

It’s hard to argue with the power of the premise, taken from the novel of the same name by Daniel Kraus, who co-wrote the film with director Brian Duffield. The singularly nightmarish predicament sits just on the right side of plausible for things not to feel too ridiculous, and to warrant plenty of post-viewing chat with friends about what you might do in such a sorry situation. That is, if you can persuade anyone to watch it with you – not a single person of my acquaintance took up the spare ticket I had on offer, or even made it through the stomach-churning trailer.

The unfortunate star of our story is Jay, played by the up-and-coming Austin Abrams, whose recent roles could all be described as “a guy having the worst day of his, or anyone’s, life”. Jay is no natural diver, but his father, Mitt (an especially grizzled Josh Brolin), has subjected him to unwanted trips beneath the waves his entire life. Mitt is at once a belligerent silverback hammering nails of survival knowledge into his son’s brain and a spiritualist attuned to the rhythms of the California coastline where he lives, especially the local whales.

As Jay reaches adulthood and Mitt’s worsening health prevents him from diving, their relationship sours further and the two become estranged. Their rift never gets a chance to heal because, not long after Jay moves to Iowa to continue his studies, Mitt takes his own life by jumping into the sea. On the anniversary of Mitt’s death, Jay returns home and resolves to find his father’s lost remains.

None of this angst is rendered on screen with particular grace, but this didn’t initially bother me. The film needed a reason to put Jay in a whale and to give him the strength to try to get out, and a boilerplate father-son trauma plot certainly lets us get to the good stuff as quickly as possible. Accordingly, it doesn’t take long for Jay’s dive to go south – caught up in a whale’s pursuit of a squid, he is buffeted into its gaping maw. It is a testament to Whalefall’s strengths that this scene still feels agonising even when you know it’s coming.

Somehow, Jay’s situation manages to get worse once he is inside the whale. To avoid spoiling the exact nature of these travails, let’s just say he isn’t the only creature the whale has swallowed up, and things get increasingly bloody. All of this is terrifically gruesome, as is the claustrophobia-inducing movement of the whale’s digestive tract, squeezing and chewing Jay’s fragile form. If anyone has further examples of this “peristaltic horror” subgenre, do send them my way.

Once Jay is able to calm himself down, he hatches a plan to escape using only his diving gear, the jetsam in the whale and his memories of his father’s teachings. It’s an odd mix of MacGyver and Slumdog Millionaire, only slimier and built on shaky emotional ground. Jay’s internal narrative is necessarily spoken aloud as dialogue in the film, making it feel artless and detracting from much of his terror.

And in telling a conventional father-son story in the least conventional of circumstances, Whalefall often gives into a masculinist impulse at the expense of Jay’s mother and sisters, who scarcely register as anything more than stock characters. Indeed, it’s unclear why Mitt – who it is later indicated is no bigot or traditionalist – spends so much time trying to coax Jay into diving when his lively daughters may be better suited to it.

In the film’s final act, the sentimentalism shifts into a truly unbearable register, undermining the admirably grisly tone of what came before. To me, Whalefall would have worked better as a full-blown horror, rather than a quasi-mystical meditation on the flaws of our parents – but perhaps it’s just that a part of me is still stuck inside that whale.

Need a listening ear? UK Samaritans: 116123; US 988 Suicide & Crisis Lifeline: 988; hotlines in other countries.