The Gabriel Hounds — Mary Stewart

It's all a grand adventure when English Christy Mansel unexpectedly runs into her cousin Charles in Damascus. And being young, rich, impetuous, and used to doing whatever they please, they decide to barge in uninvited on their eccentric Great-Aunt Harriet -- despite a long-standing family rule strictly forbidding unannounced visits. Because when the Gabriel hounds run howling over the crumbling palace of Der Ibrahim in the Lebanon, someone will shortly die.

A strange new world awaits Charles and Christy beyond the gates of Dar Ibrahim -- "Lady Harriet's" ancient, crumbling palace in High Lebanon -- where a physician is always in residence and a handful of Arab servants attends to the odd old woman's every need. But there is a very good -- very sinister -- reason why guests are not welcome at Dar Ibrahim. And the young cousins are about to discover that, as difficult as it is to break into the dark, imposing edifice, it may prove even harder still to escape.