The 7th Guest: Infection is a puzzle game for two players based on the microscope game from The 7th Guest. The game is played on a Reversi/Othello-grid, but with a 7x7 grid rather then 8x8, where the objective is to end up with more pieces then the opponent. Each player starts with two game pieces, known as microbes or cells, in diagonal corners. The player can make two possible moves each turn, either creating a new microbe adjacent in any 8 directions to a current microbe, or move a microbe two positions away, and losing the original position. In any case the destination has to be unoccupied, and all of the opponent's microbes adjacent to the new cell will be captured by the player who moved the cell.

Infection can be played against Henry Stauf, the main antagonist from The 7th Guest, with 7 difficulty levels. As in the original game, Stauf often taunts the players between moves. There is also a Mono Y Mono option where two human players can play together on the same device, and a Demo mode where the AI controls both players.

The game was created as a stand alone game partly because the iOS version of The 7th Guest lacked this puzzle, due to technical obstacles.

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