A military cargo plane crashes in London, scattering its highly classified contents across the city. Unaware the city is in lock-down, Charlie (Noel Clarke) and Shelley (Antonia Campbell-Hughes), with best friends Mark (Colin O'Donoghue) and Nikki (Laura Haddock), are at Storage 24, dividing up their possessions after a recent break-up. Suddenly, power to the building dies and they realise, horrified, that something is trapped in the dark maze of endless corridors with them...something deadly. Something alien. In a place designed to keep things in, will they live long enough to find a way out?