Accidentally swinging around the sun into a time warp, the Enterprise's crew recover from their turbulent journey and find themselves in Earth's atmosphere in the 1960s over North America. Jets are dispatched to bring the 'UFO' down, and one is caught in the ship's tractor beam and begins to break apart. The pilot, Captain John Christopher, is beamed out of his plane before it disintegrates and is welcomed to the Enterprise as the crew prepares to return to the 23rd century. Kirk tells Christopher that he cannot be returned to his own time because he has seen too much of the future, but Spock discovers that Christopher will have a son who will be very important to the history of the space program and Christopher must be returned to 20th century Earth.
