Cheered by this thought, Harry skimmed through his copy of Advanced Potion-Making and found a heavily corrected Half-Blood Prince's version of An Elixir to Induce Euphoria, which seemed not only to meet Slughorn's instructions, but which might (Harry's heart leapt as the thought struck him) put Slughorn into such a good mood that he would be prepared to hand over that memory if Harry could persuade him to taste some. . .

Chapter 22