In 1479 DR, following the request of her son Arclath Delcastle, Marantine agreed to house Amarune Whitewave and Elminster Aumar's party in her house for a time. She also told them about the Imprisoners and the creation of the Blueflame ghosts, which she knew of thanks to her family dealings with the church of Mystra.
In 1479 DR, in order to lure out Elminster after the matter of Castle Irlingstar, Manshoon sent a contingent of his death tyrants and several of his magically dominated nobles to attack Delcastle Mansion. In the fighting, Lady Marantine was fatally injured. She died soon after seeing her son a final time.
Arclath had a frosty relationship with his mother, who seemed more interested in being pleasured by young men than in the family business.