Incredibly, this game ends the first Keen trilogy by having you invade the homeworld of the alien enemies from previous games, where you proceed to lay waste to their entire civilization. You literally conduct a candy-colored one-kid genocide against this race of puppy-dog looking aliens (who you have been told are actually peaceful and merely being mind controlled!!), blasting your way through apartment buildings, cutting down whole families, shooting up a schoolhouse (kids, schoolmarm and all) with "KILL KEEN" translated into their language on the blackboard, and eventually progress to their military installations and the secret base of their mysterious controller. The idea that you're doling out this pint-sized holocaust against goofy aliens as Billy the precocious pre-teen is extremely funny and the scenario actually makes for many interesting new level designs, given that each area is roughly based on an everyday location (or the alien equivalent thereof). Some of the levels are a little too cute to be much fun, and the difficulty has been ratcheted up again. But the final boss is cool, and the whole idea is too fresh for the series and amusingly disturbing to be denied. They really went for it with this one!