MacKenzie's Promise by Catherine Spencer

Life has led Mac Sullivan to promise himself two things: never get involved with other people’s problems — or with women. He’s stuck to his guns until now, when Linda Carr begs him to find her baby niece. As an ex-police detective he has the skills to help her. But what about the prospect of an emotional search in the company of a beautiful woman whom he’s wanted since the moment he laid eyes on her?

Mac knows there’s no contest when it comes to one of his vows: a child is missing and he will track her down. But can he stick to his other promise — and keep Linda at arm’s length?