Two vacationing Illinois couples, John and Bea Miller and David and Beverly Wells, follow a detour down a backwoods road in a southern state. Terry Adams, a wealthy playgirl from Pennsylvania, drives down the same road, accompanied by schoolteacher Tom White. The cars arrive in the secluded hamlet of Pleasant Valley (pop. 2,000) where the townspeople are celebrating a centennial. Confederate flags are flying everywhere. Mayor Earl Buckman and centennial co-chairmen Lester and Rufe insist that the six Northerners remain as guests of the town. Bea is taken by a local tough, Harper, into the woods where he cuts off her finger. He then takes her to Buckman's office where she is held down by several Confederates and murdered with an ax. Bea's husband John, escorted by a local belle, Betsy, becomes so drunk that he does not notice his wife's absence. That evening, he is executed at a town barbecue. Meanwhile, Terry and John discover a memorial plaque revealing that 100 years before, the town's citizens had been massacred by renegade Union troops. The next day David Wells is murdered by a mob of townspeople, and Beverly is crushed to death by a huge boulder while a crowd cheers. Terry and John run from the town, pursued by Harper, who falls into a pit of quicksand and dies. A local boy, Billy, divulges the hiding place of their car, and they make their escape, using Billy as a hostage. Later, they return with the incredulous police, who can find no trace of the road, the detour, or even the town. The police inform the Northerners that Pleasant Valley was wiped out during the Civil War. Back in Pleasant Valley, the decorations come down and the citizens begin to dismantle the celebration trappings, while Rufe and Lester discuss plans for the next centennial, to be held in 2065.