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Daggat (Ian Borger) is crazed Vietnam veteran who finds an unusual way to use his wartime experience to enact his revenge on the man who left him for dead in the jungles long ago. He was a "tunnel rat," invading the networks of Viet Cong tunnels and killing the enemy in them. Now, he does the same in the Indianapolis sewer system, killing sanitation workers until he can get his hands on their supervisor, Ed Chambers (Jack O'Hara), who is the man who abandoned him.