Not far into the future, a stone was found in a star — then more stones were found, and it turns out that if you combine three of these stones in the right way, you create a very valuable jewel. What's more, you can combine them in a different way to create fuel.
In Troika, you are an adventurer who has dreamed of making a fortune, so you've travelled to this star along with other wanderers. Unfortunately, your spacecraft has no more fuel, so while you'd like to create jewels, if you don't also create fuel, you'll die as the richest person at the end of the universe!
In the game, you place all the heptagonal tiles face down on the table, and on a turn you either draw a face-down tile or take a face-up tile that someone returned to the table. You're trying to collect both three tiles of the same number (to serve as fuel) and three tiles in numerical order (to transform into a gem). If you have no fuel, you can't win the game; of those who do have fuel, the player with the most valuable jewel wins.