Layton Mystery Tanteisha: Katori no Nazotoki File (Layton Mystery Detective Agency: Kat's Mystery Solving Files) takes place during the events of 'Layton's Mystery Journey: Katrielle and the Millionaires' Conspiracy'.
After the paradox destroys time, The Reds and Blues are forced to relive their pasts on loop while Genkins tries to create more paradoxes to help Chrovos escape her new confinement by Donut.