Het Verraad (Treason) is the first expansion to the game De Ontembare Stad (The Indomitable Citadel)

The tactical and strategic alternatives of Treason have grown significantly in comparison to the original "De Ontembare Stad". Luck is just a small factor in the game. The character of the Dark Master is an important new feature in the game, in fact introducing an extra player in the game. Each player becomes a chance to support the dark side or the good side. Investing in dark power increases the attractiveness of the Dark Master. New playing pieces as Watchtowers allow players to defend themselves against the attacks of the Dark Master. Giving money to the church improves the power of the good forces and gives some protection against the Dark forces. New castle cards and income blocks are a valuable new asset to the game, because the players are able to monitor their income in each category.

As the Citadel is prosperous and the number of citizens grows, rumor has it that a dark character will come inside the Citadel's walls. The Dark Master must be countered by the five Grand Masters to save The Citadel from destruction. But which of the Grand Masters are strong enough to withstand the attraction of the dark side. Since each one of them would like to increase their influence in the Citadel, one or more traitors are more likely to reveal their real character when the game draws to a thrilling finale.

Besides setting up buildings, the players are able to organise battles between the Dark Master and the other Grandmasters. The Watch towers provide protection against attacks of the Dark Master.

Compared to De Ontembare Stad, the players have more alternative strategies: investing in dark power, good power, watch towers, specialising in Grandpowers or spreading out. The players are allowed to choose if they want to take over the role of the Dark Master, but only at the end of the game it becomes clear which player has become the Dark Master.