A prominent American sociologist arrives in Brazil praising the work of a man long dead and forgotten, Pedro Arcanjo. The American regards Arcanjo as the world's greatest sociologist. Local newspapers and television stations immediately try to find out who this man was.

They go back through their files attempting to reconstruct his life and achievements. They discover that he lived in the early nineteenth century and worked at a university. He was a mulatto who wrote a controversial book on the origins of the black and mulatto people of Brazil.

He put forward the theory that the way to world peace was miscegenation, an idea violently opposed by the rulers of Brazil. He was expelled from the university and jailed. Arcanjo is shown to have been persecuted for his ideals by a racist government and to have suffered for his relationships with white women. Tent of Miracles traces the origins of racial attitudes in Brazil and contrasts them, by constant cuts, with the experiences of the present.