Islands: Sam Riley is superb as a burned-out tennis pro in this slippery summer noir

Retired tennis pro Tom (Sam Riley) once beat Rafa Nadal. It’s as close as he came to being a contender, and ten years later it’s still enough of a claim to fame to prise a free drink from tipsy tourists. In the meantime he’s parlayed his talent into the kind of job that seems like a permanent vacation: coaching at an all-inclusive resort in the Canaries. Tennis in the sunshine; a never-ending whirl of booze, drugs and girls at night. What more could any man want?

Enter Anne (Stacy Martin): slim, blonde, simultaneously distant and somehow familiar. This could be a classic film noir set-up: the dissolute dupe falling hook, line and sinker for a duplicitous femme fatale. And Tom is dissolute. We first find him passed out, face down in a sand dune, and there are so many similar scenes of him stirring from an inelegant slumber that this can properly be described as a motif. This yarn (hinging on the mysterious disappearance of Anne’s husband Dave) will function as a wake up call.

Unshaven, shaggy-haired and a couple of steps behind developments, Tom seems only dimly aware that he’s going to seed, sleepwalking through life; an amiable loser. Hardly a surprise that he keeps a bottle of whisky in his racket room, and that one quick slug is never enough. It’s a juicy role for Sam Riley, maybe his best since Control (2007). Middle age (he’s 45) has tempered his sharpness with apprehensiveness and self-doubt. His charm is wearing thin.

All that said, what’s most interesting about Jan-Ole Gerster’s absorbing film is not so much how it clings to a noir template, but how it departs from it. Despite the missing person mystery and a love triangle that we practically will into being, it’s never quite a thriller – it’s ultimately too ponderous, and too reserved, for that.

Anne may be a cipher, and not above playing on her sexuality, angrily acting up when a Spanish police inspector (a fine supporting turn by Argentinian actor Ramiro Blas) starts jumping to obvious conclusions, but she doesn’t seduce Tom in a way that her 1940s counterparts would recognise: she books her seven-year-old son Anton into tennis lessons. When Tom steps up to help the family move to a more congenial room and show them the island, his affection for the kid seems to be the primary motivation.

Indeed, a subtle and unresolved mystery lies at the heart of Islands. Although it’s never explicitly stated, it’s insinuated that Tom may be Anton’s biological father. There’s a delicious, long, lingering close up on Sam as Anne reveals that Dave’s erratic behaviour derives from a recent infertility diagnosis – and his consequent doubts about Anton’s paternity.

Granted, Tom never recognises her, but it’s implied that Anne visited Fuerteventura in her wild, party days shortly before her marriage, and from what we’ve seen of him, it’s quite possible that he wouldn’t remember a one-night stand from eight years ago (she does look familiar to one of his co-workers). What’s more, Anne booked this resort – an inexplicable choice, so far as her posh husband is concerned. Did she want to introduce her son to his real father? In their first scene together there’s a beat where she seems to be waiting for him to place her. Perhaps Anton’s gift for tennis is genetic?

Gerster winks at the more generic shadow film Islands might have been by having Anne accuse Tom of forgetting their tryst in the cable car – but this turns out to be a melodramatic speech from a cheesy TV series she appeared in briefly years ago. (Dave’s arrogant dismissal of her abandoned acting career speaks -volumes about the state of their marriage.)

If the classic noir scenario is predicated on the dangerous allure of illicit sex, Islands turns this on its head. In his position, Tom has sex on tap. But in assuming the role of the father when Dave vanishes, he discovers what he’s been missing: family, emotional connection, growth.

It’s a bold move to build an entire film around an unspoken suspicion while staving off Antonioni-ennui, but Gerster (whose well-received first movie A Coffee in Berlin, 2012, was a portrait of a younger but equally feckless fellow) pulls it off, keeping us guessing about nefarious off-screen motivations while painting a sly character study set against the elemental backdrop of Fuerteventura: gaping desert wilderness, encompassing ocean and even a runaway camel. Part paradise, part purgatory.

► Islands is in UK cinemas now.