Witchward Bound by Erin Bow

Once upon a time there was a pair of witch's helpers: a cat named Butter and a raven named Owl. The cat knows he is destined to be a great hero—just ask him. The raven wouldn't recognize destiny if she slammed into it like a window. They do not get along.
But then their witch vanishes, and Butter and Owl must quest to find her. To reunite their family, they'll have to outwit sirens and cyclops, gods and ghosts—and hardest of all, they'll have to learn to work together.
Humorous and heartfelt, the story of Butter and Owl's first adventure shows what it means to be a great hero—and what it takes to be a good friend. With enchanting illustrations by New York Times best-seller Kelly Murphy and sparkling words written by beloved, Newbery Honor–winning author Erin Bow, this tale is a classic in the making—a whimsical, witty, and warm story worthy of reading again and again.