This is a summation of episode 9 of the Landscape season 3.
Deep in the depths of Arcimen, the heroes face down a huge dracolich. They suspect she is the former mate of Broxinullst, and Gerrard rushes in, calling upon the power of Bahamut to smite her. The undead dragon immediately retreats, hiding deeper in the tunnels. The adventurers pursue, eventually arriving in a long and deeply buried building.
Mac sniffs out the scent of undeath, and is attacked by a bevy of vampires! While the group attempts to ward off the bloodsucking undead, the dracolich returns. Slowly and painfully, they weaken the dracolich, who calls for truce.
Everyone lowers their weapons and Mneneveth explains that she was imprisoned here, as Broxinullst in his madness had no memory of her true identity, instead he saw her as another rival to his conquest. Mneneveth offers the group advice and assistance in taking down Broxinullst, and she gives them directions and the secret passcode to her lair on Sigil.
The group decides to continue through Arcimen and to try and locate the remaining dragons.