Item description:

Batman and Catwoman Story Completed on Normal and Newgame plus unlocked.

Catwoman DLC - Family Jewels - 40G
Retrieve your stolen goods.

You will Begin at the Courthouse and the enemy with your loot will have a glowing diamond on him when you use thief vision.
Simply knock him out in any fashion to retrieve it and fill the red bar under your health and the achievement will unlock.