Complex sentence: Upon finding out that Despereaux has broken the law by speaking with a human, the Mouse Council banishes him to the dungeons, from where he is saved by Roscuro from being eaten by the other rats.
Split into simpler sentences: Upon finding out that Despereaux has broken the law by speaking with a human, the Mouse Council banishes him to the dungeons. In the dungeon, Despereaux is caught, but he is saved by Roscuro from being eaten by the other rats.