On this page of the Assassin's Creed Valhalla Siege of Paris guide you will find a detailed walkthrough of The Queen's Gambit main story quest.
Reward: 1,700 XP.
Follow Richardis to Lisieux
This quest starts immediately after finishing the Sister of Sorrow quest. You need to mount the horses and reach the next area. Along the way a cutscene will introduce you to a little boy.
Travel to Charles' camp with Richardis
After the meeting mount your horse, and your companion will do the same. Head towards the camp.
On arrival, it will turn out you're not welcome there. To finish the quest you need to defeat several enemies. There aren't many of them, only six. After killing the enemies you'll unlock the next quest - Honor and Enemies.