Irminric was the heir to the Bann of Waking Sea. However believing that his sister would be a better ruler than he could ever have been, he joined the Templar Order instead.
After a blood mage named Jowan esaped from the Circle Tower, Irminric received the assigment to capture him. He spent much time searching for Jowan and eventually cornered him near Redcliffe Village; however Loghain's men captured them both. Loghain gave Jowan the task to poison Arl Eamon Guerrin and the templar was imprisoned in the dungeons of the Arl of Denerim's Estate when he was caught.
After killing Arl Howe while infiltrating the Arl of Denerim's Estate, the Warden can access the northern part of the Estate's Dungeon. Irminric is found in one of the cells and is in a state of lyrium withdrawal. The Warden learns from Irminric what happened to him. He begs the Warden to give his ring to his sister, Bann Alfstanna, in the Gnawed Noble Tavern in Denerim.If the ring is given to Alfstanna, she frees her brother from the dungeon and takes him to a secure place. Later she can potentially use his testimony against Loghain Mac Tir at the Landsmeet, if the Warden brings up Arl Eamon having been poisoned by Jowan.