The pleasure here is in the fine detail, and Annan makes sure we feel every scrape of chisel on wood. The characterizations are not deep, but that's part of the genre.

Annan knows how to grip, his story accelerating with a jittery rhythm, while Radcliffe's eternal earnestness fits the bill neatly.

It's the nervy camera, hugging the characters at hip height, the better to scrutinise each locked barrier to freedom, that most successfully builds the tension.

In execution, the film’s pretty decent; though one can’t help but feel like its dedication to the minutiae of Jenkin and Lee’s escape comes at the cost of a more thorough and needed exploration of its own ideals.