Robert Geary is a thief, specialising in rare art and jewelry. His next score is a collection of jewelry bound for an auction. When a heavy exchange of gunfire ensues, several security agents are killed and Geary takes off with the jewels - two hundred million dollars worth! In a high speed pursuit, security agent Tom Seale captures Geary. But when Seale searches the car. the diamonds are missing. Trying to bargain his way out of the death penalty, Geary promises to lead authorities to the jewels. Secured onto a train, he directs them north into the mountains. When the train enters a tunnel, explosions seal off both ends.. Geary's crew has come to help him escape through a maze of tunnels that lead out of the mountain chain. Additional explosive devices are set to bury the train, its occupants and the secret of their escape. Tom Seale is their only hope. In the twisting labyrinth of old tunnels, a deadly game of cat and mouse takes Seale through a dangerous world of abandoned work areas, storage facilities and one very lethal team of thieves. Time is running out for everyone as they try to make it through the Tunnel.