After inventing a time sled at age 18, Sean Ferrell’s hero treks through history, periodically returning to a post-apocalypse party that he holds for only himself in an abandoned New York hotel. It seems like the perfect party with the perfect company until at age 38 he takes pity on a younger self, stopping the Youngster from breaking his nose in a fall and setting off a chain of untetherings wherein the past lives of his many selves are no longer following the same path—especially that of his 39- and 40-year-old selves, the Elder of which is murdered.