Romance and science in the Middle Ages are the secondary themes of the novel. They are explored through Sibyll, a beautiful young maiden, and her old father, Adam Warner. Sibyll, who is in love with Lord Hastings, is inseparable from her father throughout the story. Adam is a hypomanicnatural philosopher working for many years to complete his invention, a mechanical device that is supposed to carry out the functions of a modern steam engine. Persecuted, mistrusted, and misunderstood, he is forced to work as a royal alchemist.
The novel ends tragically with the defeat and death of Warwick at the Battle of Barnet (1471).