The game takes place on the planet Opthamalia, in the Valley of the Leepers, which the manual describes as omnivorous creatures having "two long rubbery legs, a single eye and a massive green beak".

In the first phase of the game, the player pilots a spaceship to rescue crew members stranded in the valley among the Leepers.

The Leepers must be avoided or shot, lest they leap up and consume the spaceship or the crew member it carries.

In this phase the player navigates the ship through a cave in search of a giant eyeball which must be destroyed.

Lunar Leeper was favourably reviewed in the inaugural issue of Personal Computer Games.