There are 3 books in the MacGregor series. The newest book is Lady Violet Investigates which came out in 2014.

2
Once Upon a Tartan

Book cover of Once Upon a Tartan
Tiberius Flynn travels to Scotland with orders to snatch his young niece away from her Highland relations. He thinks it's going to be an easy task, until he meets the feisty little girl and her fiercely protective step-aunt. A smart, headstrong beauty, Hester Daniels has no use for an English…