Trouble Never Sleeps by Stephanie Tromly (Trouble #3)
Of course I didn’t like Digby when I met him. No one does. The first time Philip Digby–the brilliant, annoying, and somehow entirely enigmatic Digby–showed up on Zoe Webster’s doorstep, he treated her like a book he’d already read and knew the ending to. But before she knew it, he’s dragged her into a series of dangerous, and marginally legal, schemes all related to the futile hunt for his kidnapped sister. A hunt that as haunted him for years. Now, a year later, Digby’s got a new lead. Sure, it could require breaking into a secret government research facility (not to mention a little light treason), and yes, Zoe could be jeopardizing her Ivy League future. But dating Digby was never going to be short on danger, and when it comes to Digby, forget the acerbic banter, steamy chemistry, and no small amount of sarcasm; it’s all about giving him the closure he so desperately needs. But what if that closure comes with a twist neither expects?