Based on a quick scan this is the lowest price I've seen recently - Part of Shopto's January Sale. Apologies if this is a repost, but it looked like the last Shopto one around this price had expired.
Professor Layton and The Mask of Miracle
The game is the fifth in the Professor Layton series, and the second in a prequel trilogy detailing the past of Hershel Layton and his apprentice, Luke Triton. The game is set in a mysterious town called Montdol, taking place a year after the events of the fourth game Professor Layton and the Last Specter, and its accompanying movie Professor Layton and the Eternal Diva. It is the first game in the series to be rendered in 3D.
Professor Layton and the Mask of Miracle is a puzzle game presented in the style of an adventure game. The player controls the actions of a group of protagonists as they move about the city of Montdol. While moving about town, players encounter several mysteries that are solved as the main plot progresses.
While investigating the town or interacting with non-player characters, the player will often be presented with a puzzle and asked to solve it. Puzzles can be accessed at any time. If at any point a puzzle should become unavailable in the main game, it will be moved to another location to give the player another chance to find it. Completed puzzles can be played again at any time in the puzzle index, a menu available from the title screen.
Players are also capable of connecting to Nintendo Wi-Fi Connection in order to download additional puzzles. These puzzles are made available weekly for a year following release, with seven puzzles made available each week; in all, 365 puzzles can be downloaded. Puzzle packages are downloaded automatically via the Spotpass function of the Nintendo 3DS.