After carving a free state for itself in war-torn 17th-century Europe, citizens of the modern town of Grantville, West Virginia, go on a quest for the makings of medicines that have yet to be invented in 17th-century Europe. The United States of Europe, the new nation formed by an alliance between the Swedish king Gustavus Adolphus and the West Virginians hurled back in time by a cosmic accident - the Ring of Fire - is beset by enemies on all sides. The USE needs a reliable source of opiates for those wounded in action as well as other goods not available in Europe. The Prime Minister of the USE, Mike Stearns, sends a mission to the Mughal Empire of India with the aim of securing a trade deal with the Mughal emperor, Shah Jahan.

The mission consists of a mixed group of up-timers and down-timers, including paramedics, a squad of soldiers with railroad-building experience, a spy, and a pair of swindlers. On reaching India the mission finds a grieving emperor obsessed with building the Taj Mahal, harem-bound princesses, warrior princes, and an Afghan adventurer embroiled in the many plots of the Mughal court. The emperor's sons are plotting against each other, and war is brewing with the newly risen Sikh faith. But in the midst of these intrigues, the USE mission finds an ally: the brilliant and beautiful Jahanara Begum, the eldest daughter of Shah Jahan. She is the mistress of her father's harem and a power in her own right who wishes to learn more of these women who are free in a way she can scarcely comprehend. When the emperor learns of what befalls his empire and children in the time that was, he makes every effort to change their fate. But emperors, princesses, and princes are no more immune to the inexorable waves of change created by the Ring of Fire than are the Americans themselves.