Alert! Sensors indicate that aliens are invading the famous red planet! Long have the conspiracy theorists predicted this. The threat to your mission is too great; you must take action. Will you be able to prevent the infectious spread of these beings bent on expanding to every habitable planet in the galaxy? Or will you play for the other side, a species trying to establish a colony on Mars, blithely oblivious to the danger their expansion represents, unaware that there are others out there eager to keep humans “where they belong” on Earth.

—description from the publisher

On Mars: Alien Invasion is a short story expansion to On Mars made in 4 chapters with 4 different modes of play.

The short story is called Alien Invasion and contemplates the following Chapters and modes of play:

Chapter 1 - Invasion - 1 vs All - 3 to 5 players
Chapter 2 - Outbreak - Co-Op - 2 to 4 players
Chapter 3 - Blackout - Co-Op - 2 to 4 players
Chapter 4 - Monolith - Solo - 1 player