The film is set in an apartment block in the present-day United Kingdom. Mark, an artist, wakes to find that he has been sealed into his apartment with no way out. There is no electricity, no water and no communications with the outside world apart from a mysterious voice over the intercom, repeating the phrase, “please remain calm, the situation is under control”. Strange figures in Hazmat suits patrol the grounds outside and set up a military tent. Mark’s neighbour, Sergei, breaks down the wall between their apartments in order to discover why they have been sealed in and try to find a way to escape. Along the way, they team up with their fellow residents, Enid, Sally and Aiden.