Leslie and his sister, Mary, are gifted teenagers who have just been reunited with their father after more than twelve years apart. Leslie's abilities include a photographic memory, the ability to leave his body and transport himself anywhere, and a knack for reading minds and communicating without talking. Meanwhile, Mary is harboring an enormous secret from everyone but Leslie: she is gifted as well.

As Leslie, Mary, and their father work to build their lost relationship through a mutual love of dogs, a villain lurks in the shadows. Sir Alastair Woodford, who illegally appointed himself as Leslie and Mary's guardian when they were little, is now facing several charges that include kidnapping. While Leslie deals with the legal issues surrounding Sir Woodford and his associates, his purpose and morality become clearer by the day. But what he does not know is that Mary's purpose is beginning to unfold as well.

The Promise continues the tale of a modest, gifted boy and his equally talented sister as they both learn to use their powers for the good of each other--and the world.