As you'd already procured the key, Surt asked you to find the secret entrance to the Adma Stronghold and to go in. You went to find the Seiren Sahnu at Nahor Lake and asked her for help. She was prepared to support you as your problem involved the Adma Stronghold. Sahnu tasked you with obtaining Spirit Drops from Alukina's Palace. She distilled Ribbit Essence from the drops, which you used to access the secret passage. The folk who had hidden inside the Adma Stronghold had all turned to undead. Villaire from the Red Sky Legion had the appearance of a child. After you vanquished Villaire, something appeared. It looked like a strange sort of seed. You reported to the Daeva Elder Heintz. He concluded that Beritra had planted this seed into Villaire's body and that this was the cause of the contamination.