Aris' brother was taken hostage by the human expeditionary force in retaliation for the disappearance of several of their number. This allowed the Mara to tempt him and possess his body. While under its influence, Tegan climbed up a tree and dropped apples on his head. The Mara inside her then exploited his desire for retaliation to transfer itself from Tegan to him.
Using him as a host, the Mara attacked the base of the expeditionary force. They trapped him within a circle of mirrors and the Mara was forced from his body. As it left him, Aris was pulled free and the Mara was killed. (TV: Kinda)