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'. The series follows Katrielle Layton, daughter of Professor Hershel Layton, who has set up the Layton Detective Agency alongside her assistant, Ernest Greeves, and a talking dog named Sherl. Together, they take on all kinds of requests to solve mysterious cases troubling their fellow Londoners.