Sixth-year Hogwarts student Harry Potter gains valuable insights into the boy Voldemort once was, even as his own world is transformed by maturing friendships, schoolwork assistance from an unexpected source, and devastating losses.The war against Voldemort is not going well; even the Muggles have been affected. Harry receives some extraordinary help in Potions from the mysterious Half-Blood Prince, and with Dumbledore's guidance, he seeks out the full, complex story of the boy who became Lord Voldemort--and thus finds what may be his only vulnerability.