A crazed historian from the USS Enterprise uses the Guardian of Forever to travel to 1777 Pennsylvania in order to change the outcome of the American Revolution by killing the Marquis de Lafayette. Kirk and company follow and ally themselves with a group of young insurgents in order to prevent this, but things go terribly wrong when Spock is shanghaied.
Spock and Uhura's shuttlecraft is drawn through a time vortex to 18th century Kentucky. With Spock injured, Uhura must seek help in a world hostile to women of her color. At the same time a new leader emerges among the Shawnee to lead an uprising against Boonesborough, threatening Daniel Boone and his family. But is Rain of Stars what he seems?
In 2269 an archaeologist digging in the ruins of the Bodie mine on Earth discovers skeletal remains dating to 1876. On the wrist of the dead man, who is wearing a green jacket, is an alien device. Its discovery sends the crew of the Enterprise into the past to Ben Cartwright's Ponderosa where the eddies of time and an alien menace are moving together to doom Ben's youngest son.