A Formidable Enemy — Mabel Esther Allan

Eighteen-year-old Isobel hadn't been anxious to visit her grandmother in Edinburgh during her Easter vacation. She thought it would be dull. But Isobel befriends an American girl, and through her is drawn into a dangerous adventure involving foreign spies and murder. How could she know that before the holiday ended she would find herself being hunted and in danger of death?

In this fast-paced mystery, modern Edinburgh and the Western Highlands are the setting for kidnapping and romance.