Guilty as Sin by Rosalind James

There are secrets. There are sinful secrets. And then there’s switching places with your twin.
Paige Hollander and her identical twin Lily stopped switching places a decade ago. But Lily’s run into trouble, and Paige is on leave from the SFPD, recovering from a traumatic shooting. It’s not like she has anything better to do, and she remembers how to be feminine. Sort of. Anyway, it’s selling lacy thongs in Sinful Secrets and playing Heidi to Lily’s goats for a week or two. How hard could it be?
For Jace Blackstone, idyllic Sinful, Montana, is the perfect escape. In this town, he’s nothing but a reclusive, black-haired stranger with an Aussie accent and a bad attitude. Not the former pride of Australia’s special forces, not a bestselling thriller writer, and not a man with no more faith in women. Right up until the day a mystery fan starts getting much too up-close and personal, and his neighbor comes back from her vacation with a personality change that knocks him sideways.
Suddenly, Sinful is looking downright dangerous. And the biggest danger of all might come in the form of flashing brown eyes, a rear view to stop a man’s heart, and a wit sharp enough to slice him to the bone.
Sinful could be getting serious.