Harry finds and then decides to do an open-air reading of some 1600s gay erotica he found under the floor of a cupboard. Painfully frank discussions of sexuality and sexual feeling ensue, and the chapter closes with Harry and Draco under the stars. Rho and James talk for a very long time about queer authors writing stories, kink and BDSM and the anthropomorphising of magic. 

Link to Wiki for Quintessence of Debauchery: https://en.wikipedia.org/wiki/Sodom,_or_the_Quintessence_of_Debauchery