Harry Potter and the Half-Blood Prince
Chapter 21 - The Unknowable Room
Harry has no idea how to get the memory from Slughorn. He leafs through the potion book, when Kreacher and Dobby suddenly appear. Dobby tells him that Malfoy very often dissappears into the Room of Requirement. Harry wants to know at all costs what Draco intends to do, but every try to get into the Room of Requirement is unsuccessful. Once when he tries this again, he meets the disoriented Tonks who tells him she had to talk to Dumbledore. But at this time Dumbledore is not at school. When Harry starts to talk about Sirius he sees tears in her eyes and he begins to think that she maybe was in love with Sirius.