No Such Person — Caroline B. Cooney

From the author of the multimillion-copy bestseller "The Face on the Milk Carton" comes a riveting thriller about two sisters -- one accused of murder, the other desperate to prove her sister's innocence ... even as she begins to doubt it herself.

Shortly after the Allerdons arrive at their cozy family cottage on the river, Lander meets and is smitten with a handsome young man, and they begin to date. But Miranda has a bad feeling about her perfect sister's new boyfriend. And when the cops come knocking on her family's front door, Miranda can't help feeling that Lander's boyfriend has something to do with it.

The police tell Miranda and her family that Lander has been arrested. But Miranda doubts the supposedly solid evidence they say they have against her sister and decides to dig deeper. There's only one problem: the more she learns, the more she wonders why everything keeps pointing to Lander's guilt.