It's a textual adventure (some graphic embellish it, but is purely decorative and has no role in the game).
You give commands usually composed by a verb plus a noun (e.g. "go north", "examine desk", "drink potion") and are told what happens ("you cannot go in that direction", "there is a pen on the desk", "you feel reinvigorated"). You have to explore the locations, collect items, use them when appropriate and in general imagine how to overcome the various problems in order to accomplish the final goal of the adventure.
You are Amos Newton, young assistant of a scientist in modern days. Using a device of unknown origin, your mind is transferred into the body of an alien being living on a different planet in future times. Such planet is going to be invaded by humans who kidnapped the alien to study him.
You will have to control the body of your host, escape and reach his spaceship in order to warn his people of the imminent invasion.