Two brothers. One mother. One big question.

Two days before her death, Jenny Elliot suggests to her fifty-year-old son Phillip that, being half Irish, he should be more careful about his drinking. Phillip, along with his brother Spencer, has grown up believing they were the fully Jewish-American offspring of Jenny and her late husband who died in the Vietnam War. Was his mother uttering some dementia-inspired fantasy, or was her true character shining through in her last moments to leave the brothers a clue to their real heritage? After her death, Phillip decides to take a DNA test.

The brothers set off on a genetic treasure hunt in search of who they really are—and what that might mean. Are they purely products of their genetics; or were they formed more completely by their social interactions and upbringing? Are they merely victims of randomness; or are they some combination of those factors? And who, exactly, is Mr. Wizard?