Rosie Hinton, an officer in the British Army and now a convicted military prisoner is on her final work detail before being released back to her unit. Along with five other detainees they are tasked with cleaning a long deserted military facility but when they arrive it gradually becomes clear that the bunker is not as abandoned as they were lead to believe. Facility 31 is a British horror film about a group from a Military Corrective Training Centre who are tasked to clean a remote, disused military bunker. Rosie, a medical doctor in the British Army has to face her worst nightmare when she discovers that the Officer in Charge is the very same Major who instigated the Court Martial which brought her to this dark and soon to become terrifying facility. Before she can prove herself a paralysing secret bursts from the depths of the bunker, threatening to tear them all apart. It will take all of Rosie's courage and determination to get them out alive of Facility 31...