Postern certainly won't trouble the Advertising Standards Authority: the program is billed as "fast, furious and as mean as they come". It is, in fact, too fast, too furious and too mean!
The object is to clear the playing area of cherries and monsters - a feat I have never achieved. You have a crystal ball to throw at the monsters, but this may not always return immediately, so make sure every throw counts.
This sounds easy; I can assure you it isn't. You see, the monsters can move twice as fast and head for you along the passage you've just dug!
The graphics are nothing to write home about, only user-defined graphics. An awful off-key tune, played before each life, nearly drove me mad. Instructions were adequate: there's not much to write about such a simple game. I had some difficulty loading - it loads at a different volume level from all my other programs.
Dinky Digger is not original, but this is the only Spectrum version I have seen. You might like to add it to your program collection, but to me it's run of the mill.