In Over Our Heads by Celeste Straub

Three clues. Two unsolved murders. One second chance at love.
Still traumatized after the drowning of her best friend ten years ago, Lara Mattson reluctantly returns to the sleepy river town of Raven Falls, Pennsylvania. Her objective is to bury her father, settle his estate, then return to Los Angeles.
And never look back.
Not even bumping into Zach Buchanan, her ex-high-school-sweetheart turned successful defense attorney, can ruin her plan.
Until they stumble across a murdered neighbor.
With Lara’s father the number one suspect and the estate tied up in the investigation, she’s stuck in Raven Falls. But when evidence surfaces linking the murder to her best friend’s alleged drowning, nothing and no one can stop Lara from uncovering the truth and finding the real killer.
Not the uncooperative detective assigned to the case.
Not the shadowy murderer stalking her.
And certainly not Zach and her not-so-dead feelings for him.
After all, what’s a broken heart if it means avenging her best friend and clearing her father’s name?