A cop on the track of a criminal finds himself in the midst of an unfinished subway tunnel, when his flashlight reveals a startling discovery: a three metre long scorpion-like BUG. With one slice of its massive tail the bug fells the man and devours him.

FBI agent Matt Pollack is brought in to investigate, and when forensics reveal the source of the problem, he turns to his friend and entomologist Emily Foster for help. Her studies have chilling results.

Matt and a team of crack SWAT commandos must go down and rid the underground of its evil predators. Once in the tunnel, the team is attacked by an army of the creatures. They retaliate with massive firepower, causing the collapse of the tunnel entrance.

Their only way out is ten miles ahead through an emergency exit. Matt and his team must get there and exterminate the bugs before they escape into the city causing chaos and destruction.