First-time feature director Ibrahim Miiro hits the ground running with this urban drama set in London; for the first half-hour, at least, it’s a film bursting with energy and adrenaline. Hannah Laresa Smith plays homeless teenager Ally who has recently run away from foster care. In the early scenes showing her chaotic street life, the camera pushes right in, claustrophobically close. Ally sleeps in the cold under a bridge by a canal and washes in public toilets. She earns a few quid as a courier for drug dealer Carol (Sallyann Fellowes), a nasty bully who fakes a mum-like warmth. I watched with an icy sense of dread, my hands clammy. Ally has no idea how at risk she is.

A confrontation finally spirals her situation out of control. After being violently attacked, Ally runs off in a panic, leaving behind Carol’s money and drugs. And it’s here the movie disappointingly shifts into a crime opera, with the arrival of drugs kingpin Ilyas (played by Lithuanian actor Gediminas Adomaitis), another black-suited, taciturn gangster in the Euro-baddie tradition. Carol darkly whispers that he’s got links to a human trafficking gang up north. Ilyas gives Carol 24 hours to find the cash – or Ally.

Terrified, Ally keeps out of sight. Her mate Josie, a few years older and hardened by life on the streets, suggests prostitution. The only person genuinely looking out for Ally is a lonely elderly man, Frank, (Mike Kinsey), who befriended her, and now turns detective to find her. The story increasingly feels unconvincing and contrived, and the ending is a bit sentimental. But Miiro directs with real confidence; he’s a name to watch.

• My Day is available from 7 December on digital platforms.