In this Bookware text adventure, based on one of the chapters of the Science Fiction short story series "The Unorthodox Engineers" by Colin Kapp. You take on the role of the protagonist Lieutenant Fritz van Noon and his band of "Unorthodox Engineers" as Dr. Maxwell Courtney asks you to try and discover the purpose of the indestructible pillar of darkness and its mysterious penumbral shadow, (hence the name "The Pen") which was (obviously?) left by an alien race on this otherwise normal planet. And you also have to solve the riddle of contra-energy. The objective of the story is outlined to the player during the opening stages of the adventure. The book with the short story that comes along with the game helps the player to better understand the story and contains some vital clues to solve some of the adventure's puzzles.