Marie Belloc Lowndes 
Chink in the Armour [EPUB ebook] 

Spooky and suspenseful. Wealthy widow Sylvia Bailey is idling around Europe when she befriends another widow who is also a gambling addict. The two decide to go to the gambling town of Lacville, despite a psychic’s warning that they will find themselves in grave danger there—danger from which at least one of them will not escape. If only they’d heeded the warning… A real, old-fashioned "page-turner", for sure. (Goodreads)