Ironhand (Stoneheart Trilogy Book Two) by Charlie Fletcher
Edie and the Gunner, a statue of a World War I soldier, have been captured by the Walker, and it’s up to George to save them. But first he must deal with the three strange veins, made of marble, bronze and stone, that have begun to grow out of his hand and curl around his wrist. Legend has it that unless he successfully completes three challenges, the veins will continue up his forearm, and eventually pierce through his heart. As George struggles to face the choice he has made, he is determined to use his power for good, even as others wish to harness it for evil. Listen to the author talk about the first book in the series.