Deep in the depths of the earth are a series of defensive caverns built by your ancestors as they retreated from the failing Sun. Generations on you, an off worlder, must fly a ship designed to destroy these ancient defences so as to save unwary space travellers from destruction.
The ship you fly has been custom-made for the job and is described as a "total aggression fighting machine armed with a standard photon cannon and a very non-standard transmuter".
By the transmuter will you succeed or fail as it can suck in raw material from anything you blast and rebuild the material into pre-programmed forms which will provide you with anything from extra speed unts, double fire power, laser or shields. So the more you blast, the stronger your ship becomes.
You must battle your way through narrow caverns whose walls as deadly as the vices they contain. It's incredibly easy to lose a life by crashing int a wall while attempting to, say, take out one of the limpet guns that make life in the caverns very difficult. You must also destroy the aliens that scream out of generators, the robots that roll along on tracks as well as hover just out of reach until they're ready to strike.
Another great arcade game this, that shows there's still life in the old scramble style of game.