In Harry Potter and the Half-Blood Prince, Dumbledore prepares Harry for the final battle that he knows is fast approaching as Voldemort is tightening his grip on both the Muggle and wizarding worlds. Together they work to find the key to unlock Voldemort's defences and, to this end, Dumbledore recruits his old friend and colleague, the well-connected and unsuspecting bon vivant Professor Horace Slughorn, whom he believes holds crucial information about Voldemort's power.