Silver in the bone

"Tamsin Lark goes on a quest to find the infamous ring from Arthurian legend to break her brother's curse"--
Tamsin Lark didn't ask to be a Hollower. As a mortal with no magical talent, she was never meant to break into ancient crypts, or compete with sorceresses and Cunningfolk for the treasures inside. But after her thieving foster father disappeared without so much as a goodbye, it was the only way to keep herself--and her brother, Cabell--alive. Ten years later, rumors are swirling that her guardian vanished with a powerful ring from Arthurian legend. A run-in with her rival Emrys ignites Tamsin's hope that the ring could free Cabell from a curse that threatens both of them. But they aren't the only ones who covet the ring. As word spreads, greedy Hollowers start circling, and many would kill to have it for themselves. While Emrys is the last person Tamsin would choose to partner with, she needs all the help she can get to edge out her competitors in the race for the ring. Together, they dive headfirst into a vipers' nest of dark magic, exposing a deadly secret with the power to awaken ghosts of the past and shatter her last hope of saving her brother....