Comparison of Velocity and Ultrasound Transit Time Spectroscopy in Cancellous Bone Phantom

A follow-up to Robert M. UnKauf's debut novel Ascension, Guardian continues to follow William O'Donnal as he finds himself embroiled in what is beginning to appear more and more like a revolt within the Seraphic ranks. Banned from dealing with Gabrielle and Michaela by an order from the Circle, Will has completed his training with Uriel. Unexpectedly, however, he finds himself challenged by words not heard in two thousand years: "Guardian. Attend."