Layton's Mystery Journey: Katrielle and the Millionaires' Conspiracy is an adventure and puzzle game of the Professor Layton series and this series seventh main game. It features Katrielle Layton, the daughter of Professor Layton. Who solved various mysteries in London in hope of finding her missing father the famous Hershel Layton.
Private detective Katrielle Layton, daughter of the famous Professor Hershel Layton, awakens from a nightmare about her missing father, on the day of her detective agency's opening. The same day Katrielle and her assistant Ernest Greeves meet a talking dog that, for reasons unknown, cannot be understood by anyone else but them. The dog explains that he has amnesia, and that he wishes for them to solve the mystery of who he really is, and Katrielle makes up the name "Sherl O.C Kholmes" for him.
The puzzles of the game will be designed by Kuniaki Iwanami, due to the passing of Akira Tago.
The official name of the game was changed from Lady Layton: The Millionaire Ariadone's Conspiracy to Layton's Mystery Journey: Katrielle and the Millionaires' Conspiracy the 4/13/2017.