It is set after Professor Layton and the Curious Village, when Professor Layton receives a letter from his old mentor, only to go to his house and find him dead. The culprit is supposed to be a box that curses anyone who opens it, and the only clue is a ticket for the Molentary Express.
The gameplay is almost identical to the predecessor in which you solve puzzles to advance in the game. In the previous game, some of the puzzles allowed you to jot down notes on the touch screen, but here you can memo on all the puzzles simply by touching the Memo icon. The hint coins return from the previous game, hidden in various parts of the game.
The Professor's Trunk
The professor's trunk returns from the previous game but is slightly different. The top row of icons are the same featuring Journal, Mysteries, Puzzle index and save the game. The Bottom row, however, is slightly different, featuring four different icons instead of three. They are Camera: a minigame where you have to create cameras similar to the painting minigame in the previous game; Hamster: where you have to create an exercise course for your fat hamster to burn off calories; the tea set, where you brew tea using a variety of ingredients to please various people; and later in the game you obtain the Mysterious Journal. Each key you get unlocks a diary entry.
Prior to the game's release in America, Nintendo sent out invitations to various women in the media in New York to attend an event where they could play Professor Layton and the Diabolical Box. Women were separated in teams of six, and the goal was to rank up more points than the other teams. The team with the most points by the end of the event would receive free Nintendo DSis. Each team had a name referencing Professor Layton.
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