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. When flipped, the Twinner, or the actual person, will automatically start speaking and thinking the language of where they are flipping into subconsciously.

In rare instances (such as Jack's), a person may die in one world but not the other, making the survivor "single-natured" with the ability to switch back and forth, body and mind, between the two worlds. Jack is taught how to flip by a mysterious figure known as Speedy Parker, who is the twinner of agunslinger named Parkus in the Territories. In the Territories, the beloved Queen Laura DeLoessian, the twinner of Jack's mother (a movie actress known as the "Queen of the B Movies") is dying as well.

Various people help or hinder Jack in his quest.