"A Dog's Purpose" is a novel by W. Bruce Cameron that explores the life of a dog through multiple reincarnations. The story follows a dog named Bailey as he experiences different lives, each time learning valuable lessons about love, loyalty, and the bond between humans and dogs. Throughout his journeys, Bailey serves various owners, including a young boy named Ethan, and faces challenges that teach him about his purpose. The narrative emphasizes the idea that dogs have a unique role in human lives, providing companionship and unconditional love while discovering their own identity along the way.