Silver In The Bone By Alexandra Bracken

Tamsin Lark is a Hollower – breaking into the ancient crypts of dark sorceresses in search of the treasures inside. Now, rumours are swirling about a powerful ring from Arthurian legend, a ring that could free her brother, Cabell from a curse. But they aren’t the only ones who covet it. As word spreads, greedy Hollowers start circling, and many would kill to have the ring for themselves. Tamsin is forced into an alliance with her rival Emrys, the last person she wants to rely on. Together, they dive headfirst into a vipers’ nest of dark magic, and expose a deadly secret with the power to awaken ghosts of the past and shatter her last hope of saving her brother.