Colbert the Mad has followed you to Amon Amrûn, where something happened to make him lose his mind after he stirred up the furious shades from their tomb while attempting to rob it.
You ask Colbert the Mad what happened here after he attempted to rob the graves of Amon Amrûn.
'Two went in and one came out. But I never came out, not really. The shades that stirred as we cradled the loot, they stir now in my mind, always.
'I can never leave Amon Amrûn. Like the shades. Soon I'll be no more than a wandering ghost, just like them.'
Amon Amrûn is in the eastern Fields of Fornost in the North Downs.
You should search Amon Amrûn for signs of what happened to cause Colbert to go mad.
Colbert awaits you at his overlook south of Amon Amrûn.
You should speak with Colbert.