Although it’s not related to the aforementioned two games in terms of characters or story, it is considered to be part of a trilogy with them, because they all share the same engine and gameplay features.
In Marsport the year is 2494 and the Earth has been under invasion by an insectoid race called The Sept for over 70 years. The only thing that’s kept them back has been a force field that surrounds the Earth, but that is in danger of being breached unless plans can be found to strengthen it.
You are Commander John Marsh and your task is to find those plans – inside the enemy-overrun city of Marsport.
The game has three distinct objectives: 1. locate the central computer, 2. acquire the plans, and 3. escape the city of Marsport with the plans intact.
As Commander Marsh explores the city he encounters two types of Sept – Warriors, which hop around, and Warlords, which are immobile and block certain routes. A variety of robots also patrol the streets, most of which are harmless, although some – like the Wardens – are hostile to everything. Enemies can be blasted with a power gun, once it’s been acquired.
Getting anywhere in Marsport means finding items and placing them in the right places – usually to unlock doors, but also to combine items, making new ones. This time the city has elevators, meaning: there are multiple floors, making the map more complicated to navigate. There are also other security systems, like bombs, that must be dealt with when passing through certain areas.
Considering that it’s been squashed into only 48K of RAM, Marsport is a pretty outstanding program. To play it now it’s maybe a tad convoluted – maybe even boring – although there’s no doubting the game’s class overall.
More: Marsport on Wikipedia