THE WHIPPING BOY by Sid Fleischman, illustrated by Peter Sis (Greenwillow: $11.74; 90 pp.; ages 7-11).

Long ago, some royal households kept whipping boys to save a naughty prince the pain of punishment. It is this unsavory piece of history around which Santa Monica author Sid Fleischman weaves a delightful yarn, rich in detail from what seems to be folkloric England.

Jemmy is the whipping boy here, a bright urchin who yearns to escape back to his happy life of catching sewer rats. One moonlight night, he finds himself on horseback with Prince Brat, trapped in the heir’s own plan for running away. What happens in that fog-shrouded forest where robbers and outlaws lurk is adventure at its best, characters at their best.

What fun it is to meet the gypsy girl with her bear and the Hot-Potato Man! And the thugs! Cutwater is the rattleboned partner of Hold-Your-Nose Billy, the legendary highwayman who roars garlic breath through a mouthful of yellow teeth. With hopes of earning a king’s ransom, these mangy outlaws chase the boys, finally meeting their destiny in an unexpected way.

Like the royal son in Mark Twain’s “The Prince and the Pauper,” this blue blood is astonished to see how the real world lives, which is pure pleasure for the reader. After all, some of us have to make beds, don’t you know? Fleischman has a lovely way of sneaking in some important morals without going overboard. When Jemmy realizes he’s lost his taste for ignorance and Prince Brat has lost his for arrogance, their growth seems absolutely natural and their friendship long overdue.

The book’s format is a blue-ribbon example of simplicity and readability: The chapters are brief and each begins with a thumb-size illustration and preview title. Some of Peter Sis’ pen-and-ink drawings are at full-page size, and all capture the hearty, imaginative fun of the story.