Early in the life of William Robert Jones III, two things change him forever. He develops an extraordinary life of the imagination, and he falls obsessively in love with a girl named Victoria. The impoverished William lives with his family in a squalid washhouse on a wealthy relative's property. William's abusive father is the town drunk. In response to these troubles, the boy dreams up and writes stories. He concocts an elaborate fantasy life that so enthralls him, he can hardly put his pen down, and even when he does, he continues to create stories in his mind. Indeed, he fills a wooden box on wheels, his "Me Box," with notebooks of stories and folk poems, and takes it with him almost everywhere he goes.

At the novel's start, William, no longer a boy, encounters Alex, an old acquaintance he had thought was dead, who imprisons him in a basement furnace room and seems driven to kill him. Alex thinks William is responsible for murdering several boys, as well as attempting to kill Alex. Seeking answers to why this would be, William's mind drifts back through time, as he recalls his earlier life. These recollections are so vivid that William experiences them as passing through a window of time, as if he were physically entering the past. The reader soon realizes that a key aspect of William's imagination is a time-travel fantasy, which stems from his longtime interest in the work of Albert Einstein. Throughout the novel, scenes alternate between William's imprisonment in the furnace room and his "revisits" to his younger life.

His boyhood brightens when he meets Victoria. They fall in love and pursue a delightful romance. She becomes pregnant, but they are very young. Knowing their parents will object to the union, they run away to a sheep ranch, where they live as man and wife. When Victoria's father, an entitled and wealthy Scotsman, finds them, he forces his daughter to have an abortion, and then carries her away to Scotland. William is distraught, but he finds a way for them to reunite on occasion. Led by William, the two concoct a childish fantasy of a kingdom in Montana that they someday will rule.

During the plot's periodical returns to the present, the imprisoned William continues to delve into his past, with the objective of discovering something he may have overlooked in his life, some clue to why Alex believes he is a murderer. Through these investigations, William comes to believe that Alex is actually the murderer, but that he has blanked out his memory of the killings. On several occasions, William vividly remembers how, as a child, he would imagine himself in Einstein's laboratory, helping the great physicist to discover new and wondrous devices. The reader realizes that these and other daydreams once helped William to escape not only the misery of his boyhood home life but also the devastating memory of molestation by a cleric.

Stories and poems written by William, which apparently come from his "Me Box," are interspersed in the novel's main narrative, helping to demonstrate that the life of William's imagination is dangerously real to him. Eventually, the differences between the actual Victoria and the one of William's fantasies emerge, even as the mystery of the murdered boys is resolved. Marked by the plot twists of a suspense story, this romantic novel leavens tragedy with humor as the reader follows William's navigation through the increasingly illusory maze of his memory.