From the inlay:
You fingers play over the studs as you dodge the bombs dropping from the Invaders and fire back destroying the attacking force. The Invaders drop towards you, a glowing saucer, operations centre of the alien fleet floats over the attacking aliens and you fire ... The battle rages on...
This game is a clone of the arcade classic "Space Invaders".
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 Bases, points per Invader 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 7K RAM.