The Inheritance Games by Jennifer Lynn Barnes

Avery Grambs has a plan for a better future: survive high school, win a scholarship, and get out. But her fortunes change in an instant when billionaire Tobias Hawthorne dies and leaves Avery virtually his entire fortune. The catch? Avery has no idea why–or even who Tobias Hawthorne is. To receive her inheritance, Avery must move into sprawling, secret passage-filled Hawthorne House, where every room bears the old man’s touch–and his love of puzzles, riddles, and codes.

Unfortunately for Avery, Hawthorne House is also occupied by the family that Tobias Hawthorne just dispossessed. This includes the four Hawthorne grandsons: dangerous, magnetic, brilliant boys who grew up with every expectation that one day, they would inherit billions. Heir apparent Grayson Hawthorne is convinced that Avery must be a con-woman, and he’s determined to take her down. His brother, Jameson, views her as their grandfather’s last hurrah: a twisted riddle, a puzzle to be solved. Caught in a world of wealth and privilege, with danger around every turn, Avery will have to play the game herself just to survive.