A valuable diamond – the Blue Lion – is on display at the Louvre and two thieves, Arsène Lupin Lupin and Lady X, both want to steal it.

The Blue Lion is played using six tiles. Each tile shows an icon on both the front and back: Lupin, Lady X, the Blue Lion diamond, or a police inspector. Each combination of two icons occurs once. One player plays as Lupin, the other as Lady X. During set-up, these tiles are arranged in a row. In turn, the players take one tile and add it to the front or the back of the line, without looking at the back of the tile. After this set-up, the players try to score points by creating special combinations of tiles. Each turn, a player can perform one of three actions to change the line:

• Switch two adjacent tiles.
• Move a tile that is on one end of the line to the other end of the line.
• Flip a tile.

If this action results in a scoring combination of three tiles, the player scores points. The combinations are:

• Sandwiching a tile showing the opponent by two tiles showing police inspectors: 1 point.
• Sandwiching a tile showing the Blue Lion by two tiles showing the player's character: 2 points.
• Creating a row of three tiles showing the Blue Lion: 3 points.

After a combination has been formed, the middle tile of the combination is removed. The opposing player then adds it to one end of the line, although he cannot score points by doing so.

The first player to score seven points wins.