When twelve-year-old Eli becomes involved with the time travel experiments that the government pressures his parents to pursue, he travels to fifth-century Alexandria, Egypt, where he meets Thea, a scholar accused of sorcery, and Clyne, an extraterrestrial saurian who is working on a homework assignment.

Time travelers Eli and Thea arrive in Missouri in 1804, where they meet Thomas Jefferson and other famous people, then Eli joins the Corps of Discovery, hoping to find Clyne so that the three friends can return to the Fifth Dimension.