The Bloodstained Key - The Heart Stones, #1

Eighteen-year-old Marianna and her family live in luxury, attending balls every night. Despite being haunted by the death of her mother and the disappearance of her fiancé, Will, she tries to remain cheerful for her sister's sake. When their father falls ill, she discovers her family is in financial ruin and fears her world is falling apart. An offer of salvation comes from the mysterious nobleman who lives isolated from the rest of the world in his extravagant, yet menacing mansion.
Lord Bludington invites Marianna, her sister, and all their friends to his home for a week full of entertainment. He impresses everyone with his charm and wit, but Marianna can't shake the feeling he is not all he claims to be. However, when her family cannot afford the medicine needed to save her father's life, she reluctantly accepts Bludington's proposal of marriage and moves into the manor. Now isolated from her friends and family, she no longer feels welcome in the eerie house.
The housekeeper is abrupt, the maids spread gossip and fear her, and the butler appears to be spying on her. Then she discovers a secret that puts her life in danger, and unless Marianna can find the courage to fight for herself, she won't make it out of Bludington's manor alive.