He-Man has been captured by the Horde, and the Rebels manage to trace his whereabouts to Beast Island, on which the Horde have a prison. As the Rebels set out to rescue him, the imprisoned He-Man finds that Force Captain Adora, who has taken the sword, has been tricked from birth into believing the Horde are the rightful rulers of Etheria. He tells her to go out and see the world, to find for herself just how evil the Horde are. She is sceptical of him, but agrees to do so. When the Rebels reach Beast Island, they face danger from the many monsters of the island and a series of traps set by the Horde, whose leader, Hordak, is interrogating He-Man about why he has come to Etheria. (thetvdb.com)