What the Dead Know by Laura Lippman

Thirty years ago, two sisters disappeared from a mall in Baltimore, never to be heard from again. Now, after a hit and run accident, a woman claims that she is the younger sister, Heather Bethany. Heather, however is being extremely cagey about her past, saying that she doesn't want her current life exposed. Is this woman really Heather? If she isn't, why does she know so much about the sisters' childhoods? Taking place over five days, with a lot of time spent retracing the family's lives over the last thirty years, Lippman has written her best stand-alone novel yet. She also writes the long running Tess Monaghan mystery series.