On a winter’s evening, a trio of unruly teenagers board a bus, ganging up on Luke Murray, threatening to kill him. No one intervenes until Jason Barnes, a young student, challenges the gang. Luke seizes the chance to run off the bus, but he’s followed. Andrew Barnes is dragged from the shower by his wife Valerie: there’s a fight in the garden and Jason’s trying to break it up. As Andrew rushes to help, the gang flees.