Click on the rope you got from the room with the bag on the floor.
"Flophone - Restricted" is a casual online Flash game from Flonga, and is playable in a browser. This adventure game uses a point-and-click interface, and has spy and detective themes. You fly to Paris to retrieve important data on a hard drive. Near the end of the game, when you go down to the Paris waterfront, you will see a shiny object in the water. To get it, you will have to use items you found earlier in the game.
Combine the rope with the magnet by clicking "Combine" and then the magnet icon. The magnet is from Plaisir Doux.
Equip the magnet by clicking "Equip" and the magnet icon.
Click "Search" and click on the water where the shiny object is. You will retrieve a briefcase from the water.