Eriadnar is a night elf Sentinel who served under Commander Anaris Windwood in Ashenvale prior to the start of the War of the Thorns. She was among the Sentinels who were out on patrol with Anaris when the two Horde rogues Rifen and Lorash Sunbeam attacked and killed Anaris. Lorash fled, but Eriadnar sliced Rifen across the torso and lopped off one of his arms with her sword, allowing Ferryn to pin him to the ground. Eriadnar quietly told Delaryn Summermoon that she was now the commander in Anaris' stead. After interrogating the dying Rifen and realizing that the Horde was clearing a path through Ashenvale to invade Darnassus, Delaryn ordered Eriadnar to run to the night elf capital as fast as she could and inform Malfurion Stormrage of the coming army.
Eriadnar shortly arrived in Darnassus and, after being fed and tended to by some priestesses, met with Malfurion and informed him of the dire news. The archdruid thanked her and said that once she was rested, he would have another task for her. Eriadnar accompanied the first few refugees who traveled to Stormwind City from Darnassus via portal. There, she delivered a message to Tyrande Whisperwind, informing her of the Horde's attack on Ashenvale, and told King Anduin of Malfurion's orders to evacatuate not only Darnassus but also Darkshore. Tyrande said she would accompany Eriadnar to Darnassus, but Eriadnar knelt and said something heartfelt to Tyrande in Darnassian, moving the high priestess and causing her to embrace the Sentinel. After meeting with the newly-arrived refugees, Tyrande declared that she would instead stay in Stormwind for the time being, and Eriadnar instead returned to Darnassus with Mia Greymane.
Eriadnar and Delaryn reunited near the border between Ashenvale and Darkshore after Delaryn's forces had fought the Horde's soldiers in the forest for days. The two of them embraced, and Delaryn thanked Elune that Eriadnar had survived.