As a high ranking, and very persuasive auror, you have been assigned the task of searching Hogwarts for signs of Dark Magic and DeathEater action. You have Carte Blanche to search any office. Where would you begin and what would you be tempted to confiscate?
The entire contents of Filch's Office. With what he confiscates off students, he will have done the work for you, so you can walk outside the school gates, disapparate to the MOM to hand in your booty and be home early for tea.
*confused* Lupin has a chest of drawers in the staff bathroom? :P
Carte Blanche is the name of a local very popular 'investigative journalism' tv show. When I saw the title I thought this was going to be an expose on the shocking going-ons at Hogwarts complete with tearful interviews and people holding their hands in front of the camera going 'no comment'.
More likely to be 'Novem Vestementem Emperorium' where the person in need slips a few drops into food or drink of everybody that they intend coming into contact with, who then see or do not see whatever the potion applier intends, eg walking around naked while the person under the influence believes them to be dressed in flippers, lycra mankini and pink tutu - or possibly the latest designer gear.
Problem lies in administering sufficient drops, lest the effect wears off whilst in the middle of whatever they are up to.
Beware the diary of a malicious witch, I would recommend casting a revealing charm: "specialis revelio" with 3 clockwise loops of the wand after the incantation; this will reveal the presence of any magic. The more focussed the incanter the more effective it will be so it might help to meditate in advance.