When and how does Hermione end up naked?

Draco's plan

Walking in complete silence Draco sneakily walked up to Hermione's bed head, he managed to sneak all the way into griffindor dorms for this sole purpose, he made numerous plans, got the right instruments and made deals with the right people, now was time to make it happen, he couldn't let a impure blooded mage act so prideful and humiliate him, he was going to teach her a lesson she's going to remember and make and example of her to everyone.

She slowly slid the drawer of her night table and took her wand replacing it for other "special" wand he had brought with him, the he closed the drawer again, he looked at her sleeping peacefully, he really despised her, before leaving he took from his pocket a mi pouch containing some kind of magic dust and blew it in her face, "soon you will find out, granger, that some embarrassments are more humiliating than others hehehe" he said and left as sneaky as he had entered