Buried Under Ice by Cynthia Eden

Once she was falling in love with him, but now she hates him.
FBI Special Agent Oliver Foxx lied to Lark Lawson. Lied, used, seduced, and betrayed her. Four ultimate sins. The special agent got close to Lark just so that he could prove her twin brother was guilty of murder. Correction, multiple murders. The deceitful special agent believed that her brother was a serial killer, and now, because she let the wrong man get close, Lark’s brother is rotting in a jail cell. Her fault, but she’s going to fix things. Or die trying. Though she’d really, really prefer not to die…

It’s up to Lark to prove her brother’s innocence.
Lark knows her brother isn’t guilty. He is the only family she has left, and she is not about to watch him go down for crimes he never committed. So now she’s determined to hunt down the real killer. No one seems to believe that she’s up to the task, but when danger begins to stalk her, it’s clear that Lark has attracted someone’s attention. To a deadly degree.