Twelve Men's Morris, the abstract strategy game, gained widespread attention on the popular TV show 'The Devil's Plan.' Although the show referred to it as 'Nine Men's Morris,' the version they showcased was actually 'Twelve Men's Morris,' the model provided here. 

This "Twelve Men's Morris" set features a baseboard with slots, where each piece fits securely. This design element serves multiple purposes:

1. Secure Piece Placement: The slots ensure that the pieces stay firmly in place during gameplay.
2. Compact Storage: The pieces can be stored in their respective slots when you're done playing.
3. Travel-Friendly: The inclusion of a snug lid makes this travel-friendly.
4. Optimized Print: The 3MF allows for optimized multicolour printing of the base, lid and game pieces.

Twelve Men's Morris is the perfect game for those who love strategy, especially those who have enjoyed its depiction in 'The Devil's Plan'.

How to Play Twelve Men's Morris:

1. Objective: The main goal is to form 'mills'—alignments of three pieces in a straight line—and remove your opponent's pieces from the board. The player who either reduces their opponent to two pieces or blocks all possible moves wins the game.
2. Setup: The game board consists of a grid with intersecting lines and 24 intersection points. Each player starts with 12 pieces (or 'men'). Players decide who goes first by a coin toss or mutual agreement.
3. Phase 1 - Placing the Pieces: Players take turns placing their pieces on any vacant point on the board. The aim during this phase is to create mills while preventing the opponent from doing the same. When a mill (a row of three pieces) is formed, the player can remove one of the opponent's pieces from the board, except for those in a mill, unless no other pieces are available.
4. Phase 2 - Moving the Pieces: Once all pieces have been placed, players take turns moving their pieces to adjacent points along the lines. The same rule applies: forming a mill allows a player to remove an opponent's piece. The key strategy in this phase is to block your opponent's moves while trying to realign your pieces to form new mills.
5. Flying: If a player is reduced to only three pieces, that player's pieces can 'fly' to any vacant point on the board, not just adjacent ones. This rule adds a twist and can turn the tide of the game.
6. Winning the Game: The game ends when a player either has only two pieces left, has no legal moves during their turn, or if the same position is repeated three times (indicating a draw).
7. Strategy Tips: Focus on both offence and defence. While forming mills is crucial, it’s equally important to block your opponent. Flexibility and adaptability are key, as the game's dynamic changes after each move.

"Twelve Men's Morris" is a game of wits and strategy, perfect for those who enjoy a mental challenge. The rules are simple, but the gameplay is deep and engaging.