When a Jack Russell Terrier named Mrs. Henry (known to her friends as "Mac") takes a drink from an ancient, forgotten cup in a South Dakota cabin, she doesn't just quench her thirst—she gains a voice and a mission.

Stolen from Jerusalem by Vikings in the 10th century and hidden across the rolling hills of the Midwest, the Holy Grail is back. Now, Mac must guide a mysterious songwriter through a landscape of memory and music to help him find his voice and fulfill a destiny that will echo for generations.