Vietnam, 1968: Desperate to deal with the Vietcong's resistance in endless networks of tunnels, the United States creates a specialised unit trained in underground warfare. Armed with only handguns, flash lights and knives, this elite band of men are known as 'Tunnel Rats'. Following an ambush on his platoon, Sergeant Vic Hallowborn (Boll regular Michael Paré) sends his men underground to flush out the enemy. But as they blindly crawl through these darkened passageways littered with spike pits, drowning pools and homemade mines they soon realise that their mission is near impossible. The Vietnamese that inhabit these tunnels are faced with an equally grim existence, forced underground with their wives and children by the relentless bombing, they must resort to living a subterranean life lying in wait of the next attack.