In the 13th century, the Chinese expedition of Tohtai and Li discovered America. Patrolmen Everard and Sandoval received from the Danellians - creatures from the distant future, the true masters of the Time Patrol - a task: to organize the failure of the expedition. Otherwise, it may turn out that the Mongols will take over America and history will take a different path. The patrolmen killed the horses, burned the expedition's ships and forced its members to settle in America forever.