Marsport is the first (and ultimately only) game in an unfinished trilogy set in the 25th century. Humanity is at war with the Sept alien race, and they are now in a position to invade Earth, as they have the plans for their protective sphere. You play John Marsh, a soldier turned leader who must go to Mars and locate the original plans.

Marsport uses the same game system as Tir Na Nog and Dun Darach, although a 3D effect is incorporated into the graphics. A single path is displayed on screen at a time, and the view is rotated at junctions. The Warriors and Warlords must be shot down using weaponry, making this Gargoyle's most action-driven adventure up to this point.

The Marsport is split into ten distinct sections with their own functions, such as Stores, Administration and Computers. There are robots to interact with, for gaining information or objects. Pairs of objects can be combined to manufacture new ones. A central computer locks out many sections until it can be found and disabled. You will have to shoot the Sept before they can touch you, and also be wary of Warden robots which may malfunction and mistake you for a Sept.