Young veterinarian Rachel Goddard's world begins to crumble when a client rushes into the animal hospital with a dog struck by a car during a thunderstorm. The woman's terrified child, drenched with rain, loses sight of her mother in the flurry of activity and screams, "Mommy! I want Mommy!" Instantly Rachel is hurled back in time to a day in her own childhood when her baby sister, Michelle, uttered the same cry while thunder crashed and rain poured down on them. The unearthed memory feels like a fragment of a nightmare, and Rachel doesn't understand its meaning or the anguish it stirs up in her.

When she seeks answers, she learns nothing from Michelle or from Judith, their loving but manipulative mother. Judith is a psychologist who is only too happy to have her adult daughters still living in her elegant Tudor house outside Washington, DC. But their apparently serene home is a house of secrets where Judith's unspoken rules forbid questions about the family history or the daughters' long-dead father. As more baffling memories surface, Rachel begins to suspect that nothing about her family is what it seems.

Fighting her mother's attempts to control her, Rachel embarks on a quest that takes her not only deep into her own memory but also halfway across the country. The truth she uncovers will shatter her world and force her to make an unthinkable choice.