- “I tried to stay loyal, but I couldn't. I can't.”
Cairn comes from a small Free Marchian village called Wrenwith, located north of Kirkwall. He left his family behind to become a templar. It is implied by Nyree that he and the other templars of his order were very cruel to the mages in their care, torturing them for information, willing to cause so much pain that they had to cover the torture chamber's door with runes "to block out the screaming."
Cairn was tasked with apprehending a Saarebas who got separated from Arishok's group sometime between Dragon 9:31 and 9:34. Along with a group of templars, they arrived in Wrenwith, a small village, once home to Cairn. Upon arrival, they find the the Qunari mage Saarebas burned the village to the ground. Cairn's sister died in his arms. The death of his family fills his mind with the thought of vengeance. He stands out against the Chantry's orders to keep the murderer alive in order to learn the Qunari magic secrets from him. With a heavy heart, Cairn assaults the secret prison located deep beneath Kirkwall, where the man responsible for the death of his family is imprisoned. Upon the assault, however, he falls to the Qunari, unwillingly allowing his escape. When Cairn comes to, he realises the mage had escaped along with several other prisoners. To catch the man, he sets out to bring them to justice.
He meets Tallis by chance when the two cross blades trying to apprehend the same individual who was involved with the escaped mage. He tells the assassin that he is acting an agent to Chantry and he is to apprehend the fugitive. She catches his lie, when she puts in question the idea of the Chantry sending only one man after a group of prisoners. He attempts to duel the elven Qunari after she kills his charge, though eventually he leaves in pursuit of the escaped saarebas, warning her not to cross his path again.
However, he once again encounters Tallis when she saves his life, when he arrives at a Dalish camp after he follows the Saarebas's phylactery, stolen from the prison. Shen Tallis offers cooperation in finding the rogue mage, he agrees. They make a deal to duel for custody of the Tal-Vashoth when they eventually find him. The pair are joined by an elven mage, Josmael, who is attempting to locate his kidnapped betrothed, taken by the Qunari.
Cairn locates the saarebas in a cave, where he uses the blood of Josmael's love to complete part of the Mask of Fen'Harel. Though, the mage manages to escape and seal the group in the cave, alongside one of his cohorts: a reaver mercenary named Nyree.
Once they manage to leave the cave, the party - now joined by the Nevarran - is ambushed at an inn they take their rest at. The group of mercenaries was hired by the saarebas, and it comes to light that it was Josamel who led them into the trap.
Cairn accuses Josmael of betraying them and attempts to kill him, but is prevented by Nyree. Nyree reveals that she witnessed Cairn enter the saarebas's cell before the escape. The templar, forced to reveal that he inadvertently helped the mage escape, explains that he had gone to kill the mage to avenge the death of his family, but instead accidentally freed him from his bond and was overpowered. The shared secret brought the party together, and united they set out for the final confrontation with the rogue mage.
While lying in wait for the saarebas at Sundermount, Cairn has a conversation with Tallis about their purposes for hunting the mage. He insists that the saarebas needs to die, and encourages Tallis to abandon the Qun and become a renegade like he is, a Tal-Vashoth. Tallis is repulsed by the idea, but does not resist when Cairn kisses her.
After the saarebas arrives, Fina betrays Josmael by alerting the mage to the group's presence. While the group battles, Josmael stabs Fina as Saarebas used blood magic to make him so, completing the ritual and tearing open the Veil. Before the power of the Fade can be completely unleashed however, Tallis shatters the Dalish artifact, sealing the Veil shut.
Cairn confront the saarebas, who shows no remorse over killing his family. He overpowers him once again. The mage then goes on to battle Tallis ho shattered the mask. He unleashes a fatal bolt of lightning at her, but Cairn throws himself in its path, saving her life. To revenge his death, Tallis fulfills Cairn's wish and kills Saarebas.Cairn's body is burried by Tallis, Nyree, and Josmael the following morning atop Sundermount.
It is not possible for Cairn's home village to be located north of Kirkwall, as north of the city there is only land, and Saarebas supposedly beached after the Qunari ship was sunk by Isabella at sea in the south.