Firewing by Kenneth Oppel
Kenneth Oppel concludes the Silverwing trilogy in this amazing story where the stakes could not be higher - The earth heaves and splits in a terrible quake and Griffin, a Silverwing newborn, is sucked into a fissure deep below the earth. Shade, Griffin's father, soon realises that his son has been drawn into the Underworld, and embarks on the most dangerous of journeys to rescue him. Shade knows he must find Griffin quickly, but something else is hunting Griffin - a deadly foe Shade hoped he would never see again. Who will find Griffin first? And will they survive the perilous journey back to the land of the living?