This book is a chapter book about a mad rumor going around in an elementary school about an alien from outer space. The children occasionally run from the school after a student screams, "The Green Man Is Coming!" The faculty and administration are upset and are trying to prevent these mass exoduses from the school. The students soon dub one day as "Green Friday" and anticipate the sighting of The Green Man. They perform all sorts of weird rituals to keep him away. However, the tension becomes extremely high during the week of Green Friday. The book ends with the appearance of The Green Man. However, he is not an extraterrestrial being, but a "citizen of the future" who has returned to the past with a noble mission. What is his mission?