School nerd Martin helps three school friends, Mike, Geoff and Frankie avoid a school field trip to Wales by taking all three of them, along with his dream-girl Liz (Thora Birch), to an old underground bunker. Together the teenagers party non-stop for three days in their sound-proof shelter, but when Martin doesn't return to let them out, the party atmosphere changes quickly into a living nightmare. Liz is found a few days later walking towards the school, covered in blood and traumatised. She is taken to a police psychologist where she tells her story; but when Martin is later picked up, he gives a very different account.