Fear Street Sagas - Heart of the Hunter

A medicine woman tells Jamie Fier that she knows how he can win the heart of the girl he loves, but it will cost him. She gives him a potion to drink, and that night, when the moon is full, Jamie is mutated into a wolf. With each full moon, he metamorphoses again, but if his true love sees him while he's in the form of a wolf, he'll remain a wolf forever.