The key slid into an ancient looking keyhole with a click, and Una gave it a fierce twist. The door opened a crack, and Una gritted her teeth as she pushed hard on it with her shoulder and made her way through. She found herself on a path that zigzagged up a steep hill. Over the top, a long walk away, she could see the outline of a lone turret.
This is it. Una was in enemy territory now, and she wouldn't leave until she had discovered the Enemy's plans.
- from the back cover
I love this series. Highly recommended!