The Rescue (Guardians of Ga'hoole #3)

Ever since Soren was kidnapped and taken to the St. Aegolius School for Orphaned Owls, he has longed to see his sister, Eglantine, again. Now Eglantine is back in Soren's life, but she's been through an ordeal too terrible for words. And Ezylryb, Soren's mentor, has disappeared. Deep within Soren's gizzard, something more powerful than knowledge tells him there's a connection between these mysterious events. In order to rescue Ezylryb, Soren must embark upon a perilous quest. It will bring him face-to-face with a force more dangerous than anything the rulers of St. Aggie's could have devised-and a truth that threatens to destroy the owl kingdom.