The Mirroring of Mary King is a two-player game in which one person is a mortal contemporary woman named Mary King and the other player is the ghost of Mary’s long dead ancestor, a 17th century Scottish merchant burgess of the same name. While on a week’s holiday in Edinburgh, Mary visits Mary King’s Close where her presence attracts the spirit of her long dead ancestor, now a hungry ghost that wants to live again in Mary’s body. The two Marys engage in a battle for control of the living Mary’s mortal body.

Players use control cards and power cards to exert their influence on Mary King’s psyche, represented by 12 tiles arranged in a 4 x 3 grid. These tiles are flipped back and forth throughout the game as the players gain and lose control of them.

The game progresses over five days, starting on Monday and ending on Friday. Each player gets one turn each day, with the ghost player always going first. As the week progresses, the mortal and the ghost become more exhausted and more desperate: the number of control cards each may play decreases and the number of ideas they may pursue increases. At the end of each player’s turn, both players suffer penalties based on the tiles of Mary that their opponent controls.

A player may immediately win the game by completing their image of Mary using the 12 tiles, or if their opponent runs out of cards. If neither player completes their image of Mary by the end of Friday, the winner is determined by a scoring system based on their remaining cards and their control of Mary.