Deadly sub-atomic particles are running free in a scientific research centre. It is your job to trap the darting Leptons using a robot craft before your time runs out. As you move the craft across the screen, a green ion-trail is dragged along behind. When you reach the edge again, the smaller area confined by this green line, is filled in. A Lepton is captured if it is trapped in this area or if 95% of the screen has been filled. A bar running along the bottom of the screen indicates the percentage of the total area remaining to be filled. Enclosed areas are coloured red, but at any time, you can switch to the faster speed and areas so filled are coloured pink.

Higher levels introduce Chasers which move along the borders. A life is lost if you collide with one of these or if a Lepton hits your trail. The number of Leptons and Chasers increases up to a maximum of 5 of each. An extra craft is obtained on completion of the third, sixth and ninth screens.

A good strategy is to build small, narrow pink blocks up the centre of an unfilled area in fast mpde and then to finish off using the slower mode to reach the top of the screen and capture the Lepton.

The base score for a fast-filled screen is 1237 - double for slow-filled areas. By way of example, the maximum score that can be obtained on screen 7 (if 95% area is filled and all Leptons captured on slow-fill) is calculated as follows: Score: 1237 x 0.95 x 2 (all slow-fill) x 5 (screen multiplier) x (1 plus 3) (3 Leptons captured) = 47006. This is excluding the time bonus.

Z - Left, X - Right, : - Up, / - Down
SPACE sets the robot craft in motion. Pressing this again causes the craft to move faster. S toggles the sound on and off before each game.