It's Christmas time, and the trio are still looking for information on Nicholas Flamel. Harry tries to find information in the library's restricted section, but is caught and kicked out by the librarian.
When Christmas Day actually arrives, Harry receives a surprise gift (among several mundane ones) in the form of an invisibility cloak that used to belong to his father James. There is no indication as to who sent the cloak as a gift. Harry uses the cloak to his advantage and once again sneaks into the restricted section. This time, he comes across a screaming book, and as he is leaving, he comes across Filch, Snape, and a mirror with a mysterious backwords incription: "I show not your face, but your hearts desire," or "Erised stra ehru oyt ube cafru oyt on wohsi." He is startled to see his deceased parents in the mirror, rather than himself.
When Ron looks into the mirror the following evening, he sees something entirely different: a vision of himself with the Quidditch Cup. The evening after that, [[MrExposition Dumbledore]] explains to Harry that the Mirror of Erised shows people what they want to see, but that it is also dangerous because it has driven wizards to insanity in the past. He warns Harry to never go looking for it.