The Lying Game by Sara Shepard
At first The Lying Game may seem like an updated version of The Parent Trap but I hold much hope in this new series from the author of Pretty Little Liars.
A pair of estranged twins meet and foster child, Emma agrees to cover for her wealthy twin sister, Sutton while she drops off the face of the earth for a little while. At first Emma, enjoys her sisters fiercely fabulous lifestyle but in not much time at all she realises it's all a facade and there are many long-buried secrets harbouring beneath the surface. When Emma longs for her old life of a close-knit family and adoring boyfriend she discovers Sutton may not be coming back at all.
The Lying Game will be released December 2010 by HarperTeen.