Two important types of relationships in The Thief Lord are family and loyalty. In addition, the relative quality of age, or people’s relationships to each other and to time, also drives the plot of this fantasy novel.
The protagonists, Prosper and Bo, are brothers; they are family who are related by blood. They become involved with a group of children who are orphans. Although they become involved in illegal activities, primarily theft, they develop a strong loyalty to each other, constituting a community similar to family. Scipio, however, violates the trust within the group because he is not poor or an orphan, and he lies to the others.
Through a series of events, the brothers encounter Ida, who thwarts their plan to steal from her. Both the planned theft and the intervention involve the boys with a magical carrousel. Its power is to change people’s age. The person who commissioned the theft, the Comte, has his age changed by the carrousel. Scipio also uses this power. Whereas the Comte is change from adult to child, for Scipio the reverse occurs. Some plot lines converge in different ways because of this age change. The Comte disappears, but the now-grown up Scipio gets a job. Prosper and Bo, rather than return to their abuse relatives, enter a new family arrangement with Ida.