The crystals provide power to the castle's defences. The crystals are also able to summon creatures, like dragons. Orcs that consume the energy of the crystals are attacking the castle and absorb the energy from the crystals. But adventurers have arrived to stop it.
In this game, you have to hire adventurers using your funds, to get the list of adventurers you need to press the grey button (the red button hires the fighter, who fights using a sword, the blue button hires a thief who fights using a bow, he is stronger than the fighter, and the green button summons the warlock, he casts a magic bolt which kills the enemy in one hit, the warlock also fires faster than the thief). They leave after 30 seconds.
Orcs spawn every 4 seconds and they absorb the energy from the crystals. If one crystal runs out of power, it's game over.
You can also use bombs, to use bombs, press the button in the bottom centre. You have to choose the location where you will place the bomb. To place the bomb, press the right mouse button. You can kill an orc with a bomb if he passes the defense.
Right to the bomb button, there is a red button, if you press it and have enough power in the crystals, you will summon the dragons.
Some clickable supplies may spawn, like bombs and energy, to get them, you need to click on them.
To pause the game, press the button in the top left corner.