Sherlock Holmes Chapter One

Missable. You must do this first, and attempt to dress up as the theif second.

At Mrs. Nini's, after grabbing all the disguise materials, go to the right wall in the back room and observe the photo hanging on the wall. Jon will then prompt you to prank Mrs. Nini by dressing up as the man in the photo.

While in the wardrobe section of the menu, have Sherlock change into the following:

White Suit
Top Hat
Long Sideburns
Old Man Make-Up

Then, go talk to Mrs. Nini. You'll get the achievement!