A lifeless body awaiting immortality. Magic that erodes a sister's identity. Enemies bent on retribution. Bridget has saved her sister, Dahlia, from imprisonment. But their reunion has come with enormous costs. Their friend was murdered in the rescue efforts, and Dahlia herself is no longer fully human. Together, they seek to grant their friend a second chance at life. But the magic that will save him also paints a target on their backs.

As the sisters race to uncover the key to resurrection, Dahlia's former captors pursue them-coveting the ancient powers and seeking justice for their own fallen companions. At the same time, they must also contend with how Dahlia's immortal life, new abilities, and fracturing personality are changing their relationship forever. UNDENIABLE is the second book in The Grigori Cycle. Multi-Hugo Award-winning author Mary Robinette Kowal called UNRELENTING "a tapestry of emotion that effortlessly weaves together the threads of grief and obsession.".