"Keen Must Die! is the third Commander Keen game in the series.
Keen travels to the Vorticon homeworld in search of the mysterious Grand Intellect that has directed the Vorticons toward Earth. The game features the cities, parks, and suburbs of the Vorticons, and their women, children, pets, and mechanical toys make up the enemies. The Vorticon alphabet is also decoded in a school house, allowing for the player to travel to the other in-game locations and read the Vorticon signs."
Source: Wikipedia, "Commander_Keen," available under the CC-BY-SA License.