Twice upon a Time — Allen Appel

For the second time, historian Alex Balfour, who has a genetic disposition to time travel (Time After Time), finds himself in another era. Transported to the Philadelphia Exposition of 1876, Alex is befriended by a disparate group, including four black men, some captured Indians, Mark Twain, and General Custer. Concurrently, his contemporary lover, New York Times reporter Molly Glenn, is pursuing the story of a young Sioux claiming to be the descendant of Crazy Horse.