Low on fuel you land your space craft on an asteroid in order to replenish the Dilithium Crystals, known colloquially as 'Diamonds', which power the craft. The Snargs here own a Diamond mine and you need to steal all the available diamonds in order to refuel your ship.
You must dig into the asteroid using joystick 1 but must be careful about dislodging rocks. If you are quick you can pass beneath one rock but two stacked on top of each other will surely get you. Failing stalactites in the lower cave and a drawbridge in the upper cave also present hazards. For two players, there is a Snarg guard which can be controlled by joystick 2. He can patrol existing tunnels but cannot dig his own.
Oh, yes, while you are digging, a Snarg tank is blasting away at the rock bluff behind which you landed and if you are not quick enough, you will have no ship to go back