Before Portelaine will introduce you to the three High Houses, he wants you to perform a third task for him.
This quest is available if you have completed the quest Men of Honor.
Starting the Quest
Talk to Portelaine in the Observatorium in Coerthas Central Highlands to begin the quest.
Recover the Stolen Wares
Go southwest to where the orange arrow is pointing in the minimap. Examine the first two sparkling Stolen Wares, then enter the purple circle around the third Stolen Wares.
Defeat the three Hooded Assaulters, starting with the one wielding a rod, then the one with the lance, and finally the one with the sword and shield.
Afterward, examine the third Stolen Wares.
Report to Portelaine
Go northeast to the Observatorium and enter the first building on the right, and talk to Portelaine to hand over the stolen wares and complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Carrilaut to accept the next quest: The Rose and the Unicorn.