You are in a spaceship under the influence of a fluctuating gravitational field, which makes said spaceship extremely difficult to control. You are opposed by three killer balls which roam around threatening to destroy your ship with a single touch. To proceed to the next level you have a task to complete, then the exit door opens.

The first three levels involve connecting power stations with laser beams without blocking yourself off from the exit or blowing yourself up. You drive to a live (rd) power station, touch it, whereupon your ship turns red, drive to a dead power station and touch that, whereupon the two stations will be connected by a beam.

Touching various blocks brings on differing effects. The Apple block changes gravity, numbered pieces add to your score; skulls kill you stone dead. Then there's the alcoholic block - an enemy which jumps around randomly and knocks you into skulls. There is a tight time limit of 90 seconds to each task.

You can choose between two types of spaceship. One can be brought to a halt by pressing the Fire button, the other is for experienced players and maniacs only; it tends to run out of control as it cannot be braked without a lot of joystick waggling.

That, essentially, is all there is to the plot. At first the game looks extremely simple - then the subtleties slowly appear and you find you can't put the joystick down. Its secret is the mixture of fast action and strategy. On most levels there are a few correct ways to complete the task but plenty of opportunity to go wrong, even without any nasties to distract you.

The graphics are stunning. Bright reds, greens and blues are used to great effect, but the real showstoppers are in the patterned backgrounds in the style of Arkanoid. Some are animated. Seeing foreground graphics, then the mid-ground oscillating behind them and a static background behind that makes a terrific impression.

Text is displayed in a large, clear font and the display fills the whole screen. No corners have been cut - even the menu screens are well presented. You never have to touch the keyboard, its joystick selection for everything.

Sound quality lags not far behind. There is a short, delicate passage accompanying the loading screen, then some loud and rhythmic tunes on the menu and high score screens plus wonderful effects during the game - a screech of brakes as the spacecraft slides to a halt, the clang of metal on barrier and much more.

Beam is one of the best games I have played on any computer.