Jim Darcy, the pilot of an X-15 rocket-powered research aircraft, and his wife, Linda, become trapped 10 seconds ahead of their time, enabling them to watch time unfold to catch up with them at the rate of about one second every 30 minutes. In the time left before returning to synch with normal time, they see that their daughter, Janie, is about to be hit by a rolling military truck whose parking brake had not been set. Jim and Linda's inability to move objects in the "real" world prevents them from resetting the truck's parking brake or pulling young Janie out of danger. Their problem is aggravated as they soon learn that at the moment when time "catches up" with them, they must assume the exact positions they had been in five hours earlier, when this whole thing started, or they could remain in that state forever.

They meet an unnamed and seemingly malevolent individual (Kay Kuter, but only identified as "Limbo Being" in the cast list) who earlier experienced the same situation, but failed to make it back in time. When it reveals that it could take from them their chances to return to reality Jim and Linda come to see just how grave their situation is: one or both could end up being stuck in this state forever.

On discovering that he can move and manipulate items in the crashed plane and car, Jim hits upon a way to save his daughter from death. He removes seatbelts from his wife's car and ties them to the back wheel of the menacing truck. He then ties the other end around the brake lever so that the truck's brakes will engage the moment the time warp ends. (It was, by that time, moving at 10 mph.)

With no time to spare, they hurry back to the crash site and assume their original positions. When time catches up the seatbelt pulls the emergency brake, stopping the truck. Their daughter is safe, the world returns to normal, and no one is the wiser.

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Wikipedia