She's Not There — Joy Fielding

A vanished child, a family in turmoil, and a fateful phone call that brings the torments of the past into the harrowing present ... the New York Times bestselling author of "Someone Is Watching" weaves these spellbinding elements into a gripping novel of psychological suspense -- a must-read for fans of Laura Lippman and Mary Higgins Clark.
 
“I think my real name is Samantha. I think I'm your daughter.”
 
Caroline Shipley's heart nearly stops when she hears those words from the voice on the other end of the phone. Instantly, she's thrust fifteen years into the past, to a posh resort in Baja, Mexico -- and the fateful night her world collapsed.
 
The trip is supposed to be a celebration. Caroline's husband, Hunter, convinces her to leave their two young daughters, Michelle and Samantha, alone in their hotel suite while the couple enjoys an anniversary dinner in the restaurant downstairs. But returning afterward, Caroline and Hunter make a horrifying discovery: Two-year-old Samantha has vanished without a trace.
 
What follows are days, weeks, and years of anguish for Caroline. She's tormented by media attention that has branded her a cold, incompetent mother, while she struggles to save her marriage. Caroline also has to deal with the demands of her needy elder daughter, Michelle, who is driven to cope in dangerous ways. Through it all, Caroline desperately clings to the hope that Samantha will someday be found -- only to be stung again and again by cruel reality.
 
Plunged back into the still-raw heartbreak of her daughter's disappearance, and the suspicions and inconsistencies surrounding a case long gone cold, Caroline doesn't know whom or what to believe. The only thing she can be sure of is that someone is fiercely determined to hide the truth of what happened to Samantha.