Jack Sawyer, twelve years old, sets out from Arcadia Beach, New Hampshire in a bid to save his mother, who is dying from cancer, by finding a crystal called "the Talisman." Jack's journey takes him simultaneously through the American heartland and "the Territories", a strange fantasy land which is set in a universe parallel to that of Jack's America. Individuals in the Territories have "twinners," or parallel individuals, in our world. Twinners' births, deaths, and (it is intimated) other major life events are usually paralleled. Twinners can also "flip" or migrate to the other world, but only share the body of their alternate universe's analogue.