The Lives Of Christopher Chant by Diana Wynne Jones
In this enchanting fantasy novel, a young boy discovers his remarkable ability to travel between worlds while he sleeps. Unbeknownst to him, his gift makes him a valuable asset in the eyes of his uncle, who uses him to smuggle magical artifacts. As the boy grows, he learns more about his powers and the ethereal realm known as the Related Worlds. He must navigate the complexities of his family's expectations, his unique abilities, and an impending magical conflict. With the help of a talking cat and other peculiar friends he meets along the way, he embarks on a journey of self-discovery and must decide where his loyalties lie and how to use his gifts for the greater good.