From the inlay:
You are flying over the surface of a distant planet under attack from aliens and your fuel is running out. You thrust upwards blasting aliens from the sky and downwards bombing fuel dumps and ground bound ships. A landscape of mountains, plateaus and valleys (randomly produced) slides under your ship as waves of aliens descend from above and rockets fire up at you from the ground.
This game is loosely based on the arcade classic "Scramble", though with a randomly generated landscape.
Like many Quicksilva games for the ZX81, the game is provided with a list of POKEs which can be used to modify parameters such as the number of enemy ships on-screen, points per fuel dump destroyed, etc.
The game can take advantage of either or both of two Quicksilva peripherals. A QS Character Board was a peripheral which allowed alternative characters in place of the ZX81s standard character set. These could then be used to display alternative shapes as graphics rather than using letters, numbers and simple blocks to make up the display. The other was the QS Sound Board. The standard ZX81 had no sound output, the QS Sound Board provided audio output for the game.
The outside of the inlay states "For the ZX-81 with 16K RAM" however the instructions state that the basic game requires a minimum of only 4K RAM.