When Morgana suffered from nightmares and showed signs of possessing magic, Merlin suggested that she seek the advice of Druids. On her journey, she was surrounded by Serkets against which Aglain defended her and brought her to safety. While he tended to her, he reassured her of her safety and reunited her with the druid boy, Mordred, who had been able to sense her distress, leading to her rescue. Mordred offered to take care of Morgana and asked Morgana about her reasoning for appearing in the forest, at which point Morgana revealed she sought their help. Meanwhile, Uther issued the order for all of the prisoners to be executed, so Merlin went to find her while Arthur and the knights were looking for her 'kidnapper'.
Arthur and his men found the site of Merlin's campfire and continued on, as Merlin secretly worked his way into the Druid camp. Morgana asked the Druids why she was able to see the future and start fires with her mind, and Aglain confirmed that she had the gift of magic. He told her she should not fear her powers, assuring Morgana that she was safe with the Druids and that she would learn more about her powers in time. Noticing smoke from the site, Arthur and his men then descended upon the camp while Merlin tried to convince Morgana to return to Camelot. Arthur's men attacked the camp and, in the chaos as the Druids fled, Arthur assumed Morgana was being kidnapped when she ran with Aglain and Mordred. As a result, Aglain was shot and killed by a knight as he tried to escape (The Nightmare Begins).
Aglain was a gentle, kind hearted man who helped look after Morgana after she was injured by Serkets. He told Morgana that she could use her magic for good indicating that he believed magic was a good thing.