Winter Holiday follows the adventures of Walker siblings (Swallows) and Blackett sisters (Amazons). Brother and sister Dick and Dorothea Callum meet the Swallows and Amazons during the winter beside the lake. They become part of the group, and join in their play of Arctic expeditions. The holiday is extended when leader Nancy Blackett catches mumps and the group is quarantined and cannot return to their boarding schools. Initially, while waiting for snow to fall, the children embark on a series of adventures ranging from rebuilding an igloo to building an ice sled. Dick displays heroism by rescuing a sheep belonging to Farmer Dixon stranded on an ice-covered ledge, thus gaining his gratitude and earning them a sledge of their own.