Nico - Nico's Apartment, Gallery | Paris Broken Sword: TSC Guide

You will be visited by an Elderly Man, wanting you to help him find the stolen painting. Nico will show Marques the pictures she took herself.

Examine the photos closely

Look at the one in the bottom left corner, captioned Thief. This will unlock the "Ink Trail" achievement. Have a look at the Badly Framed Photo too. The elderly man will take it. Don't forget about the other two. Afterwards, leave the room. When the cutscene ends, you'll be in the corridor with the intent of finding the key to your neighbor's apartment. Look under the Door Mat, but you won't find the key there. Instead, examine the Floor Crack and use your press card on it. The key will stick to the gum that's still on it. Click on the doormat again, then use the Apartment Key to enter the Neighbour's Apartment.

Nico will lend the elderly man her neighbor's apartment

You'll head to the Gallery area. Talk to Laine in the café, and when he asks you out a date, say yes. You'll find yourself in the gallery's monitoring room. Sit down on the sofa next to Hector (click on it). You'll need to distract him so that you can have a look in the Folder, which is under the seat next to Hector. Talk to him. Pick a Glass of Champagne and your romeo will fill two glasses.

Laine has obviously not noticed the folder

Click on your glass and it will be put in your inventory (Champagne). When you use it on Hector, Nico will spill the drink all over him. The poor fellow will leave to clean the stains ("Suited and Fluted" achievement). Grab the folder from under the seat. Read it, but put it back. A long cutscene will trigger.