Later, during the Time of Troubles, Lord Mourngrym Amcathra, fearing the threat of the god Bane in Zhentil Keep, ordered Thurbal to go and spy on the evil city. Thurbal discovered that Bane wanted to invade Shadowdale, but he was greatly injured in his escape from Zhentil Keep. He was trapped in a recuperative sleep throughout the Battle of Shadowdale.
After the battle, he awoke cured. Thurbal was chosen by his lord to be the defendant of Adon and Midnight in a trial over the presumed death of Elminster Aumar. Thurbal was convinced of the innocence of Midnight and Adon, but the mob believed his judgement be twisted from his time in Zhentil Keep. In the end, Midnight and Adon were condemned to death.