This quest is acquired from a skeleton which can be found immediately to your left as you pass through the first Eluvian to The Crossroads during the Trespasser main quest. Once you have the map from the skeleton, you will be able to find four statuettes in The Winter Palace courtyard. The locations of each are shown in the screenshot below.
Note: This is a hidden quest, which means it won’t show up in your journal. You will therefore need to track your own progress once you have the map from the skeleton.
When you have found all four statuettes, return to the skeleton at The Crossroads and interact with it to complete the quest.