Its Breath is Worse than its Bite

Fight the Gargoyle, being mindful of its breath weapon which can petrify you. The breath weapon has two forms: an arching horizontal spray with short range and aerial blasts with longer range but easier to dodge. Both have visual cues. The safest strategy is to wait for the Gargoyle to begin its breath attack, then move to its flank and attack.

After defeating the Gargoyle, return to Gran Soren and speak with Aldous.

Aldous will inform you that the duke has noticed your work and has more tasks for you, warning you might be away from Gran Soren for a while. Accept the task.

Go to the Duke's Solar (upstairs along the western side of the castle) and speak with the duke.

Follow the duke to the treasury. He will unlock an ornate chest if you returned the real Wyrmking's Ring. The chest contains a Paladin's Mantle.

Trigger a cutscene (a non-interactive cinematic the game plays automatically) by heading for the door. A guard will report that Salvation has taken Greatwall. The duke postpones the expedition and tasks you with vanquishing Salvation. You will receive a quest reward and the achievement/trophy 'The Message'.

Loot the treasury: find approximately 53,500 gold around the ornate chest, a Golden Bastard in the east square chest, and a Badge of Merit in the west square chest. In the north-western corner near two urns, find a Grand Surcoat.

Leave the castle and find Mirabelle, Aelinore's hand-maiden, along the northern stairs just outside the castle.

Mirabelle will give you a 'Set of Royal Guard Armor' to disguise yourself and asks you to help Aelinore escape the Blighted Manse in the Northface Forest.

Equip the Royal Guard Armor and head to the Northface Forest. The bridge to the Blighted Manse is north-west of the Traveler's Rest and south-east of the Healing Spring.