There’s a really tight zombie horror in there somewhere. It has some good ideas, and one or two decent jump scares. The monsters are sufficiently gruesome, with enough black blood and jerky movements to make you squirm. Overall the plot feels about fifteen minutes too long, but needs twenty minutes more story? They play fast and inconsistent with the rules of their own story. Typified by the confusion we feel around their physical location, where the people are within the architecture of the prison. It’s just not clear. On the plus side it has a majority female cast, but it does lean heavily on a few zombie horror tropes, forcing some of the the characters to be realised as stereotypes. What this film needed were fewer characters, a clear plan by the lead, basically a much tighter screenplay.