The Pendragon's Champions

The fickle god Mabon, loose again in the human world, searches for the Thirteen Treasures of Britain. With each one he collects, his power grows. Knowing that time grows short, Cade sends out his champions to draw lords from throughout the land together for a final stand against Mabon--before it is too late.
The Pendragon's Champions is the fifth book in The Last Pendragon Saga.
The Complete Series reading order: The Last Pendragon, The Pendragon's Blade, Song of the Pendragon, The Pendragon's Quest, The Pendragon's Champions, Rise of the Pendragon, The Pendragon's Challenge, Legend of the Pendragon.