Do you get the popup about "Solemnly Swear..." when you exit the office? When I first got Q5, I clicked on the map, and there was a spiel about "Magical Barriers", then I "remembered" that it's a Marauders' Map, and said the Passphrase, which causes some locations' names to be in a different color.
If so, go to 'Corridor (and have some Leviosa Fun with the Blonde)', 'Corridor Above Archway Below', 'Bath with Moaning Myrtle', and 'Gryffindor Common Room', then go back to your office. There should be a Slytherin girl waiting for you with a task.