After hearing what Lupin had said, Roy grew curious about the map Lupin had made during his school days. Filch's Office happened to be upstairs, and since it was afternoon and Filch was out, Roy decided to drop by and ply his old trade.
Arriving at the closed door of Filch's Office, Roy gave it a push and found it locked-just as he had expected with Filch away. Delighted, Roy checked that no one was around, drew his wand, and aimed an "Alohomora" at the lock.
Under the spell's influence, the door to Filch's Office clicked open.
Roy pushed the door open and stepped inside, taking in the cluttered office. Only then did he realize that the prank items Filch had confiscated over the years had already filled every corner of the little room. Faced with the mountain of assorted prank supplies, Roy hesitated. If he disturbed the pile, Filch might well notice someone had burgled his office when he returned.
As he considered this, Roy's gaze fell on a locked drawer beneath Filch's desk.
"What have you got in here?"
Roy stepped forward and tugged at the drawer. Finding it locked as well, he raised his wand and cast another Alohomora.
"More prank supplies, huh? And here I thought Filch might collect something interesting. Wait, is this the map?"
Roy immediately spotted a bundle of crumpled paper at the top of the drawer. Unfolding the old parchment, he actually sensed magical fluctuations coming from the large, unassuming sheet.
"This should be it."
Roy carefully checked his surroundings to make sure no one would wander in, then drew his wand and recited the incantation as Lupin had instructed.
"I solemnly swear that I am up to no good."
What an interesting password. Lupin must have been a lot like Fred