After you retrieve Leia's egg from the would-be thief, Luquelot expresses his concerns to you.
This quest is only available if you started the game in Gridania, and you have completed the quest Leia's Legacy.
Starting the Quest
Talk to Luquelot in Bentbranch Meadows in the Central Shroud to start the quest.
Deliver Luquelot's Letter
Go back to Gridania and talk to Miounne in the Carline Canopy. Hand over Luquelot's letter and there will be a cutscene.
Next Main Scenario Quest
After completing the quest, talk to Miounne to accept the next quest: To Guard a Guardian.