1st Lieutenant Jake Tanner (Jan-Michael Vincent) shares ICBM silo duty at an Air Force missile base in the California desert with Major Eugene "Sam" Denton (George Peppard) who is requesting not to work with him. On their way to duty Major talks to Airman Tom Keegan (Paul Winfield), an aspiring artist. When the United States detects incoming nuclear missiles, Tanner and Denton launch part of the retaliatory strike, initiating Doomsday.
Two years later, the Earth has been tilted off its axis by World War III, radiation has mutated insect life, and the planet is wracked by massive storms. Tanner has resigned his commission and has been scouting Barstow while a likewise de-commissioned Keegan has been painting as an artist in one of the base's out-buildings. An airman falls asleep in a bunk and drops a lit cigarette onto a pile of magazines which causes the entire base to catch fire and explode, with no Air Force survivors. Keegan and Tanner are unscathed as are Airmen Denton and Tom Perry who were in an underground garage bunker. Denton has been considering going to Albany, New York to find the source of a lone radio transmission.
They set out in two Air Force "Landmasters," giant 12-wheeled armored personnel carriers capable of climbing 60-degree inclines and operating in water. They must cross "Damnation Alley," considered "the path of least resistance" between intense radiation areas. On their journey, they lose one Landmaster in a storm (which also kills Perry), pick up two survivors, fight a band of crazed shotgun-toting mountain men and encounter mutated "flesh stripping cockroaches" in the ruins of Salt Lake City which eat Keegan alive. A tidal wave set off by earth returning to its normal axis (amid energy storms in the night sky) occurs right before they reach a surprisingly intact Albany.
