The court starts to worry, as the queen, who has arrived for nearly two years, hasn't been able to produce any descendant
to king D. João V, of Portugal. The solution comes in the form of an old franciscan friar, that makes the king promise that if he is given the long awayted descendant, he would command the construction of a convent for the order in the town of Mafra. The daughter was born, and the promise must be kept.
The book, framed by this context, tells the story of Baltasar "seven suns" (sete-sóis), a disabled soldier and man of war, and his wonderings, firstly arround Lisbon, where he meets Father Bartolomeu Lourenço, who dreams of flying like a bird, and Blimunda, a young woman, only daughter of a woman convicted by the Inquisition as a witch. She has, like her mother, psychic abilities, she is able of looking to a man's inside and see his "will". Father Bartolomeu, when takes notice of this, finds in her just the right instrument to acomplish his dream. He engages both of them in the project, Blimunda is to collect enough "wills" to set the
machine he has drawn to floatation, and Baltasar is to build it while he leaves in a journey of knowledge to master the secrets of flying. After his return, the word is out that the
priest is to build such unholy device, the inquisitors persecute them, but only to find them gone, along with the machine in which they escaped. They manage to land in a covered hill and hide the feared machine. Baltasar and Blimunda set off to Mafra, his hometown, but Bartolomeu disapears.
In Mafra they witness the progress of the works in the convent, and from time to time manage to visit the machine, in hope of seeing the priest one more time. On one of these times, Baltasar goes alone, but unwillingly puts the machine in motion and it takes flight. Blimunda worried goes after him, but only to find the site empty and with little signs of Baltasar. She begins a journey in search of him that will end in Lisbon nine years later...