How much knowledge has been lost over the centuries—over the millenia? And how differently would we view the world had we a better understanding of its past? Little is known of Shiva's life and deeds, yet the heretics venerate her as a saint. Ser Aymeric's ancestors are said to have founded Ishgard by the will of Halone, yet he admits that scripture only tells so much. Ultimately, however, the details of his people's war with the dragons are irrelevant. Regardless of how the conflict began, it is destined to continue—unless Iceheart's plan succeeds, which the Scions cannot allow. While Minfilia and the others search for a means to breach Iceheart's sanctuary, you are to assist Yuyuhase and the 3rd Unit Braves in tracking down the heretics who attempted to ambush the allied forces.
The heretics were last seen heading towards Daniffen Pass, and the 3rd Unit Braves are already in pursuit. Yuyuhase leaves to join them and bids you follow. Do as bade and speak with any 3rd Unit Braves you find.
Many of the 3rd Unit Braves are unaccustomed to the frigid conditions in Coerthas, and the young man you find kneeling in the snow is no exception. Having twisted his ankle, he is no longer able to keep up. Press on without him and join the others south of Daniffen Pass.
You come across several sets of tracks which appear to belong to the Braves and their quarry. Follow them southwest and keep your eyes peeled for both friend and foe.
You find a solitary Brave. Though not seriously injured, he is clearly disoriented and in no condition to fight. According to him, the heretics split up, prompting the Braves to do so as well—and Yuyuhase followed one trail alone. Search for the officer in the woods to the east.
You rescue Yuyuhase from certain death, slaying Iceheart's followers before they can deliver the telling blow. Speak with the Crystal Brave and confirm his condition.
Yuyuhase reveals that he was able to slay one heretic, and was in the process of searching his victim's body when the dead man's comrades surprised and overpowered him. With a grin, he then produces a piece of parchment and proceeds to read you the message written thereon. It would seem to be an escape plan devised in the aftermath of the heretics' failed ambush at Snowcloak. The plan mentions a rendezvous point near the Observatorium, as well as a merchant sympathetic to the heretics' cause. Search the outskirts of the Observatorium and seize the fugitives before they escape.
Outside the walls of the Observatorium, you chance upon the merchant and a single heretic, who subsequently attempt to flee. However, they are stopped in their tracks by the unexpected arrival of Captain Ilberd, Alphinaud, and Yugiri. After Ilberd takes them into custody, Alphinaud explains that they had been seeking the merchant in connection with their investigation into the Ivy. Wait with Alphinaud outside the gates while Captain Ilberd interrogates the merchant.
The interrogation of the merchant is not expected to take long, but Alphinaud is doubtful that it will yield any useful information. The Ivy would surely not be so careless. Be that as it may, all you can do now is wait and hope that your fellow Scion is wrong.