R.I.S.K. (Rapid Intercept Seek and Kill) is set on the planet Christon 3 where scientists work on developing new weaponry. Of course the planet gets attacked by aliens and the player, as a pilot who is nearby, has to drive them back.

In many ways a Defender variant, the game is a horizontally scrolling shooter (the player can move in both directions) and the goal is to clear the levels of all aliens. However, there are certain distinguishing features, notably an upgradeable space ship.

The game begins in a secure station where the player can repair damage or upgrade the ship. When everything is ready, a map is shown where the next target sector is chosen from. Inside a level, a mother ship might drop supply pods, which either repair the ship, fill up ammo or contain ship parts. In each level, it is also possible to land the craft and allow one of the scientists to climb in. After a level is clear, the player returns to base through an underground tunnel. Here there are no dangers, only narrow platforms on which the player should try to land. A successful landing allows one to choose from ammo, ship parts or blueprints. Certain combinations of parts, blueprints and picked up scientists are required to upgrade the ship. Possible upgrades include faster speed, better fire power or shields.