Four teenage gangstas break into a shopping mall to evade a confrontation with a rival streetgang.
Their evasion turns into a short-lived "shopping spree" until police arrive. Fleeing the police, the teenagers head for cover in the mall's basement.
They become lost in the labyrinthine basement -- apparently a bunker system from WWII (indeed, some of the tunnels date back to the Maori Land Wars).
Unable to find their way out, the teenagers are stalked and killed, one at a time, by a thing that doesn't want them there.