Multiple alien races have discovered Earth. Two members of one of those races, “Chiddy” and “Vess” of the Pistach, approach Benita Alvarez-Shipton and ask her to carry a device to the authorities that will communicate their message. Benita uses this as an opportunity to escape her abusive husband. The device ultimately reaches the U. S. President, and the Pistach envoys arrange a personal meeting with him. Having noticed Earth's forays into space, the Pistach envoys have been sent to evaluate Earth for membership in a confederation of intelligent races. Failing to qualify for membership exposes Earth to sequestration from space travel and predation by the three other races that have become aware of Earth. The envoys point out some issues that Earth needs to resolve and then take various actions to assist with those problems. The envoys also insist that Benita act as their official intermediary. Throughout the book, one of the envoys, Chiddy, explains the history of Pistach and their religion in journal entries. The Pistach religion and way of life are driven by the stories revealed in the eponymous Fresco, a series of seventeen painted panels. Age and soot and grime have darkened the panels beyond recognition, so the Pistach rely on the Compendium which contains annotated copies of the Fresco panels. When rebel Pistach take possession of the Fresco and clean the panels, it is revealed that the stories told in the Compendium are contradicted by the actual paintings, threatening the entire body of principles on which Pistach society is based. To prevent the Pistach from withdrawing their protection of Earth, Benita and a group of artists from Earth put the Pistach to sleep with sarsparilla and secretly repaint the panels to be in accordance with the Compendium. The changes to the panels are acclaimed a miracle.
Library Journal notes "Tepper's talent for creating believable human and alien characters lends power and credibility to her work and makes her a convincing portrayer of sociologically oriented sf." Booklist states that the latter half of the book "stretches the limits of credibility" but concludes that "she has created an overwhelmingly detailed scenario for humanity's first contact with aliens." Kirkus describes it as "consummately skillful, wise, sometimes hilarious, iconoclastic performance, although possibly too relentlessly polemical".
