In a sinister effort to ground our space program, a hostile planet has cast an impassable shield around the earth. Even if a ship gets in, it never gets out. Gargantuan sentinel ships, defended by waves of attack saucers, saturate the shield with aoutrageous weaponry: Zig bombs, chargers, chirpers, trackers, blockers and bounce craft. You are the Beamrider, on a courageous journey to clear the 99 sectors of this Restrictor Shield.