Jill Quint, MD 07-Castle Killing

Being shoved out of a castle tower is a terrible way to die....
A close friend of the mystery-solving foursome is murdered when he's pushed out of a window of the castle's clock tower minutes before their planned meeting in a Cardiff pub.
Jill, Marie, Angela, and Jo are wondering why Nick is late for their meeting in a pub on the first day of their vacation. He lives in Amsterdam and is always on time. Jill feels a sense of dread when she sees two men in suits enter the pub and ask the bartender a question. The men are pointed their way as they're the only Americans inside. The detective inspectors introduce themselves to the foursome, hoping to question them only to find that Jill's team begins their own search for Nick's killer.
The mystery follows them through Wales and on to Edinburgh as the team tries to figure out just who Nick is. He's not who they thought he was and so is that the key to his murder?