The being trapped within Umas tortured husk turned out to be Awallac'h - a powerful Sage of the Aen Elle elves. Geralt had made his acquaintance years before. Already during these prior encounters Awallac'h had displayed an intense and, frankly, rather unnerving interest in the Elder Blood and its bearer, Ciri, His exact motives were unclear at the time, and he had made no particular effort to explain them to Geralt.
Geralt likewise had no idea what bound Ciri and the elf now. There was no doubt Awallac'h had helped her, had saved her numerous times from the Wild Hunt - but why? Alas, the Sage, quivering on a razor's edge between life and death, offered no answers to Geralt's burning questions.
He did, however, muster enough strength to utter a crucial piece of information Ciris location.
When Geralt got a chance to talk to Ciri about Awallac'h, he learned that the Sage had been her tutor and mentor for some time. They were bound by a common enemy. Awallac'h had been the chief advisor to the previous ruler of the Aen Elle, whose demise had precipitated a conflict between Awallac'h and the successor, Eredin. The Sage had thus made it his mission to protect Ciri from his new kings malicious designs, whatever the cost.