The film’s greatest accomplishment — notwithstanding its superfluous, sequel-inducing epilogue — is the remarkable consistency of tone (director Dan Trachtenberg) with which it is constructed. It sustains a slowburn gloom throughout its considerable runtime, through its characters’ schemes, their counters, tender filial recollections, the first signs of Stockholm Syndrome, of faith, and then, the discoveries of murder, moments of violence and ultimately, the film’s renovation into a new genre.

…the movie does teach a lesson, which is that monsters come in many forms. Goodman delivers a brilliant performance, playing his good guy/bad guy part perfectly. While the story revolves around the character of Winstead, it is Stambler who steals the show, mainly due to his impulsive characterization and shifty intentions. Even with minimal set and visual effects, the movie captures a lot more than most other films of the same genre.

The film grips you from the get go and in his directorial debut Dan Trachtenberg has kept a tight rein on the proceedings. By focussing on three people in an enclosed space, he gives the grand disaster movie imagery a miss, which works well as we are imagining all manner of horrid things.

The suspense is built around the possibility of escape and the threat of what lies beyond and, worse still, within the sealed-off bunker. The climax is a bizarre and hard-to-swallow genre-shift with some plot points left frustratingly unresolved.