Mad is the Heart - Denise Robins - Google Books

https://books.google.de/books?id=6oXEAwAAQBAJ

Heiresses twice over, Viola and her young sister traveled to exotic Khartoum to be with their guardian, the sophisticated rock-steady Lionel. But Viola's excitement was spoiled by her sister's obvious infatuation with Lionel -- and the presence of the…