A shootout with a real difference - that's Fantastic Voyage. Instead of facing waves of lamb-chop-shaped invaders or mincing meteorites, you pilot a microscopic submarine through the veins of a human body, battling against rogue white blood cells to hunt and destroy a blood clot in a brain capillary.

You are injected into a right arm and must make your way to the brain by navigating through the body's bloodstream.

Your aim is to destroy the blood clot and to do so you have four difficulty levels.

The instructions you get are on a very small piece of paper giving details of the commands you may use in the three modes of play, and a map of the blood circulatory system you must travel along.

Some heavily medical terms are used for the different veins and arteries, and I couldn't understand half of them!

I went straight into scan mode, which give me a side and front view of the patient. My submarine was a tiny dot in the right arm, where I had been injected. Also on display were my energy level, direction, and size, which gets larger the longer you stay in the body.

After a good while looking at the map, I managed to get to the right brain capillary. So I switched to view mode, where I used the L and R keys to steer along the artery; the movement of the submarine is very well done, as you see the artery walls moving past you.

Suddenly a bug-eyed monster - actually a white blood cell - moved in front of my sub, and I was automatically put into attack mode. This gave me control over the Z, X, N, M and B keys to let me move up, down, left, right and fire, as well as display the rogue white cell in front of me.

Destroying white blood cells is none too easy. They jitter about the screen at a rapid rate and you have to use laser power sparingly, as it consumes valuable energy.

Still, I got rid of it in the end, and the computer put me back into view mode to carry on the clot hunt. But I never found it!

A very good game indeed, blood clot or no blood clot. Not only is the theme interesting, but there's some very clever programming at work here. There is a good deal to do.

My only grumble, apart from the missing clot, is that there are too many white blood cells to be dealt with - and surely losing all those cells can't do the patient too much good?