Complex sentence: The Trojans dismiss Cassandra's prophecies (in the myths, Cassandra was given the gift of prophecy by Apollo, but then cursed never to be believed) but in the melee Vicki slips away and rescues Steven from the dungeons.
Split into simpler sentences: The Trojans dismiss Cassandra's prophecies (in the myths, Cassandra was given the gift of prophecy by Apollo, but then cursed never to be believed). In the revelry Vicki slips away and rescues Steven from the dungeons.