Hank Morgan, a mechanic at a gun factory, is knocked unconscious and awakens in England in the year 528. He is captured and taken to Camelot, where he is put on exhibit before the knights of King Arthur's Round Table. He is condemned to death, but remembering having read of an eclipse on the day of his execution, he amazes the court by predicting the eclipse. Later he concocts some crude gunpowder and uses it to blow up Merlin's tower. It is decided that he is a sorcerer like Merlin, and he is made minister to the ineffectual king. In an effort to bring democratic principles and mechanical knowledge to the kingdom, he strings telephone wire, starts schools, trains mechanics, and teaches journalism. He also falls in love and marries. But when Hank tries to better the lot of the peasants, he meets opposition from many quarters, including the knights, the church, Merlin, and the sorceress Morgan le Fay. He and Arthur, in disguise, travel among the miserable common folk, are taken captive and sold as slaves, and only at the last second are rescued by 500 knights on bicycles. Hank and his family briefly retire to the seaside. When they return they find the kingdom engulfed in civil war, Arthur killed, and Hank's innovations abandoned. Hank is wounded, and Merlin, pretending to nurse him, casts a spell that puts him to sleep until the 19th century.