The Lost Sun has broken free. Fin's hometown, Kluchaned Landing, is destroyed, and the Pirate River is rapidly turning into a black, stagnant swamp. The existence of all countless worlds is under threat. In addition, Fin and Marrill were faced with the betrayal of their closest friend. And now they are forced to fight him, and their allies are yesterday’s enemy. To stop the disaster, friends will have to go to the heart of the Stream! They have never climbed this far... But what if they have yet to meet the most powerful enemy?!