In the sixteenth century Portuguese Catholic missionaries introduced Christianity to Japan. The religion flourished for about fifty years, but by 1614 the Tokugawa government issued an edict that outlawed Christianity and expelled the missionaries from Japan. About 150,000 believers went underground and continued to practice their religion in secret. These people are known as the "Hidden Christians". Otaiya, meaning "Big Evening" is the Hidden Christian version of Christmas Eve. Through the occasion of this ceremony, the film tells the story of Japan's Hidden Christians. Made with the cooperation of contemporary Hidden Christians on the remote island of Narushima, the film features the only two remaining priests in the Goto Islands.