From the back of the book:Caravan of Mars is an adventure designed for 3-6 characters. The adventure involves the heroes being hired by a noble merchant that needs to extract his valuable radium shipment from an abandoned city. The heroes will have to overcome the dangers of a green man-infested city as well as the Green Wastes in order to complete their mission. Unfortunately, a nasty surprise awaits them toward the end. - BoardGameGeek