Jan Palmer, reluctant heir of the Bering Steamship Company, witnesses the murder of Professor Frobish by Zongri, a sword-wielding jinn whom the professor of Islamic culture unwittingly liberates from an ancient copper jar bearing the Seal of Sulayman. Zongri spares Jan’s life but curses him with “eternal wake-fulness” before leaving to return to the land of the jinn. Jan is unable to convince his family or the authorities that he did not murder Frobish himself and is thrown into prison.
During his first night in prison, Jan awakes to find himself trapped in the body of Tiger, a human sailor on a ship run by ifrits in the land of the jinn. Tiger and his fellow human slaves are actually corpses animated by living souls whom the jinn steal nightly from sleeping mortals but allow to return by daybreak, oblivious to how they have spent the night. The swashbuckling Tiger has a history as a troublemaker. Jan finds it increasingly difficult to suppress his mischievous personality.
Back in the waking world, Jan discovers that his business manager, Nathaniel Green, and his lawyer, Shannon, are conspiring with his domineering Aunt Ethel to have him committed so they can take control of his business empire. His only ally is Alice Hall, by day a secretary and by night a temple dancer named Wanna in the land of the jinn. She is powerless to help him.
Jan shuttles back and forth between his predicaments in the real world and the dream world, unsure of how to save himself until Tiger steals a ring bearing the Seal of Sulayman from Zongri and learns of its magic powers. At his courtroom hearing in the waking world, Jan calls for the copper jar with the seal on it and uses it to curse his persecutors with eternal wakefulness. In a titanic battle in the world of the jinn, Tiger humiliates an army led by Zongri. Jan, whose personality has begun to fuse with Tiger’s, threatens his persecutors in their jinn-world personas if they do not cease and desist in their efforts to have him institutionalized. They relinquish their claims to the family business, and Jan and Alice are married.