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 falls foul of another security measure: a book ''screams'' when he tries to read it. He flees as Filch and Snape arrive to find the intruder and hides in a disused classroom. Here he sees a mirror with a mysterious inscription: "Erised stra ehru oyt ube cafru oyt on wohsi." Read backwards: "I show not your face, but your hearts desire." He is startled to see it that the reflection shows himself standing with his parents and other deceased relatives.
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, Harry goes back to the mirror and runs into [[MrExposition Dumbledore]]. 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.