Atonement (つぐない Tsugunai) is the fifteenth episode of Phi Brain: Kami no Puzzle Season Two and the fourtieth episode of the anime series overall.
As Melancholy takes interest in a girl named Lotte and her intelligent dog named Rummy, Rook shows Kaito and the gang a newer Replica Ring model recovered from a manufacturing plant for Cubic to analyze. Melancholy equips Lotte and Rummy with Replica Rings and uses them to confront Rook in a puzzle, in which they must navigate a fog filled maze over a deadly drop, with the loser falling to his death. As Rook manages to learn the trick to solving the maze, Rummy struggles under the command of Lotte, whose personality is manipulated by the Replica Ring. As Rummy stops, Rook reminds Lotte that it's not the mazes Rummy liked, but her. As Herbert decides to set the maze to automatically collapse, Rook manages to reach the center in time to save both Lotte and Rummy. The next day, Rook returns to the POG to help stop the Orpheus Order from claiming more victims.