Dr. Manhattan sits on Mars using his precognitive powers to determine when the picture he is holding will fall the surface. He spends the next several panels thinking about his past.
He flashes back to when he was 16. He is repairing a pocket watch. His father enters the room and decides that he doesn’t want his son to take up a dying trade, and wants him to going into nuclear science, specifically bombs. He dumps the watch pieces off a fire escape.
He then goes onto for a science company. As he is being shown around, he runs into Janey Slater. The talk for a bit and she buys him a drink. He then flashes to days at the carnival with Janey, making love to her, repairing watches, and the experiment that made him Dr. Manhattan. He got locked into a test vault that separates objects from their intrinsic fields. The door has a safety feature that couldn’t get him out or stop the process. A couple of months later, weird ghost like images start to appear in the laboratories. One day, a full-fledged boy appeared. Jon was now Dr. Manhattan.
Time goes on and the government uses Manhattan as a weapon to crush any adversary they face. He meets different costumes at various times but never really establishes a relationship.
Manhattan tired to go back to his life with Janey but eventually it failed. The stress of his new powers along with his unemotional ways caused him to get with Laurie, the Silk Spectre.
He remembers being with The Comedian in Vietnam, and all the killing and violence that went on there. He remembers the lives he took there.
He then goes to see his friend Adrian Veidt in his Artic establishment. From there he recalls the Keene Act of ’77, and who got to stay masked and who was forced to retire. Rorschach did not retire. The next two pages flash a panel of most of the important moments of his life.
The story returns to the present, with Dr. Manhattan floating above the surface of Mars. From nothing arises a great castle made from his mind. He stands on the balcony of his castle and watches a meteor shower.