After Gaspard de Chalons has trapped Celene, Briala, and their companions in Halamshiral, the group decide to join forces and seek aid from the Dalish. When they are attacked by sylvans, they are rescued by Clan Virnehn. When Briala and her companions finally reach the camp of Clan Virnehn, Keeper Thelhen makes it clear that he wants nothing to do with Briala's companions or their plans, nor does he care about the city elves whom he does not consider to be elves at all (he calls them "flat-ears"). He believes that even if they help Celene defeat Gaspard in exchange for the Dales, they would only face a similar betrayal like when the Chantry declared an Exalted March on the elves centuries ago.
The Keeper says he is only interested in reclaiming their past, going to such lengths as to summon one of The Forbidden Ones, Imshael, to interrogate it so that it can help reactivate the Eluvian network.
Imshael created a Keystone that would lead whoever wielded it through a series of Eluvians that would end in a central chamber connected to all of the Eluvians in Thedas. From there, whomever holds the Keystone could reactivate the Eluvians and reset the spoken password needed to travel through them.
Imshael offered the Keystone to the clan's keeper, Thelhen, in exchange for a body to posses. Thelhen refused and imprisoned the spirit indefinitely in a stone circle prison. Imshael then tricked Empress Celene's champion, Ser Michel de Chevin, into freeing it.Thelhen, along with most of his clan, were massacred by the demon after Michel frees Imshael from its prison.