When two children with skin the color of emerald leaves appear in a twelfth-century English village, the local community must grapple with the presence of the unknown.

The protagonist, a young boy named Ralph, observes the arrival of these mysterious siblings who speak an unintelligible language and refuse all food except green beans. As the children struggle to adapt to the harsh realities of medieval life, they face suspicion from the villagers and the scrutiny of the local lord. The narrative framework utilizes a blend of historical observation and folkloric mystery, focusing on the tension between superstition and the desire to understand the alien visitors. The story explores the physical constraints of a secluded village and the logical limitations of a society rooted in rigid religious and social hierarchies.

Readers frequently highlight the atmospheric quality of the prose, which captures the isolation and superstition of the medieval period. Discussion often centers on the ambiguity of the central mystery, as the author avoids providing a definitive explanation for the children's appearance. Critics note the balance between the historical setting and the fantastical elements, which are treated with a grounded, realistic tone. The narrative is often praised for its focus on character development, particularly how the villagers' reactions reveal their own fears and prejudices. Many readers find the exploration of the 'other' to be a compelling thread that remains relevant across different historical contexts.