Another planet in the period of medieval times. An employee of the institute of experimental history from Earth, who is send under the name of noble don Rumata of Estor as a spy with a mission to contact the local resident of the institute, arrives in the city of Arkanar. But the resident perishes under an unlucky attempt to make a palace coup, and Rumata have to take his place as the resident. Soon he meets all the horrors of the medieval society - a peasant war, palace coups, mass executions. To continue to be an indifferent watcher of all these horrors turns out to be simply impossible...