The Third Twin by CJ Omololu

Having an identical twin sounds like a lot of fun, especially when you think about all of the hi-jinx you can't away with. It's a lot of fun until people die and you look exactly like the killer.

Ava and Lexi are identical twins. Alicia is their made-up triplet they've created so that they can date guys when they're just looking for a little bit of fun. It's all fun and games until one guy gets a little too hands with Lexi while she's pretending to be Alicia. Although she wants to put an end to "Alicia," Ava is having too much fun. When guys that Alicia has dated, though, start turning up dead, it's not so much fun, especially when Lexi becomes the prime suspect. While she knows she didn't do it and she knows that Alicia isn't real, the only explanation is that Ava killed these people. Is it possible that her sister really is a killer, or is there something else going on?

The novel starts off a little bit slow in building the suspense, but once the situation develops and the stakes are raised, it become a roller coaster ride as Lexi tries to prove her innocence and protect the people she cares about. The book has its twists and surprises. Some teen mysteries can be a little over the top in plausibility, but I think this novel does a good job of toeing the line without going over. It is definitely worth the read if you're looking for a suspenseful murder mystery. 
MMK