With the help of her assistant Ernest Greeves, she solves cases in and around London, alongside a talking dog that, for reasons unknown, only the two of them can understand.

After solving the case of the disappearance of one of Big Ben's hour hands at the request of Inspector Hastings of Scotland Yard, Katrielle, Ernest and Sherl investigate and solve several other cases, most of them related to the "Seven Dragons", seven of the most rich and influential figures of London, with assistance of Hastings and Emiliana Perfetti, one of the Yard's profilers.

Other cases include Hastings' request to look for a present to his wife on a holiday and solve a murder that Katrielle was wrongly accused of committing.

In the final case of the game, Layton and the Seven Dragons are invited by the mysterious Lord Adamas to the abandoned mansion of Maximilian Richmond, a millionaire who died 10 years before.

In the occasion, Adamas forces the Seven Dragons to sign a contract where they relinquish all their fortunes to him should they fail to solve a series of puzzles, or he will reveal a grave secret about them.

Layton's Mystery Journey was developed by Level-5 and directed by Akihiro Hino, with character designs by Takuzō Nagano and music by Tomohito Nishiura.

This resulted in the shift in protagonist from Hershel Layton to his daughter, Katrielle, as the development team felt that they "can't bring back a guy who's saved the world and have him go do things like find a missing cat".

[15][16] Shaun Musgrave of TouchArcade gave the game five out of five stars, praising the series's smooth transition to mobile platforms, the "outstanding" presentation, the story and the puzzles.

[23] Adventure Gamers's Jack Allin felt as though the case structure made for accessible mobile and casual gaming, and was positive towards the "pitch-perfect voice acting", as well as the visuals, and the high quantity of puzzles.

[18] On the other hand, despite the simplified narrative style, GameCentral for Metro still considered there to be little fundamental change compared to the prior titles in the series, which offered very few new ideas.