Tower is a set collection game for 2-4 players who want to race to beat their opponents to stores and buy the resources they need before the stores are out of stock. Resources are purchased with jewels, which players draw from the black bag at the start of their turns. The players then use their purchased resources to construct segments of the tower. The first player to construct all three of his tower segments wins!
A big theme of Tower is scarcity of resources, with only 18 resources in a four-player game. It's likely that in any given play session there will be enough resources for only one player, forcing everyone to play dirty in order to come out on top.
The black market provides a source for players to hire thugs to carry out some pretty shady actions. These range from intimidation, to stealing resources from other players, and robbing Salil, the tax collector. It's a dirty job, but it's necessary in order to succeed in Tower.