The Final Gambit by Jennifer Lynn Barnes

Avery's fortune, life, and loves are on the line in the game that everyone will be talking about.

To inherit billions, all Avery has to do is survive a few more weeks in Hawthorne House. The paparazzi are dogging her every step. Financial pressures are building. Danger is a fact of life. And the only thing getting Avery through it all is the Hawthorne brothers. Her life is intertwined with theirs. She knows their secrets, and they know her.

But as the clock ticks down to when Avery will become the richest teenager on the planet, trouble arrives in the form of a visitor who needs her help-and whose presence in Hawthorne House could change everything. It soon becomes clear that there is one last puzzle to solve, and Avery and the Hawthorne brothers are drawn into a dangerous game against an unknown and powerful player.
Secrets upon secrets. Riddles upon riddles. In this game, there are hearts and lives at stake - and there is nothing more Hawthorne than winning.