When is an apple more than an apple? When it's resting in Eve's palm – or better yet, in the hands of the storyteller(s) of Genesis.

The same happens to other objects touched by myth: Fire, for instance, has Genesis-sized significance in the story of Prometheus, while an ordinary ring of gold glows with forbidden power in the story of the Nibelungs (and in the tales of that splendid latter-day jeweler, Tolkien). Pick the fable of your choice, and you're bound to find a seemingly ordinary object transformed. (Or turn to Carrie Vaughn's clever, entertaining "Discord's Apple," out this month from Tor, and you'll find an entire basement full of such items in a dying man's Colorado home.)

Lawrence Goldstone's splendid 16th century thriller "The Astronomer" (Walker & Co.: 296 pp., $24) turns on another ordinary object invested with vast, ominous significance: a book.

In "De revolutionibus orbium coelestium" — "On the revolution of the heavenly spheres" — Nicolaus Copernicus posed a daunting, terrifying theory for the people of 16th century Europe: that the cosmos are sun-centered, not Earth-centered. Though the Polish astronomer's revelation today is regarded as a triumph of science, at the time, the book represented forbidden knowledge as much as Eve's apple or Promethean fire. Why? Because, Goldstone explains, it shook the foundations of theology:

" … as an axiom of True Faith, the Earth must be at the center of the universe. As Man is unique in the eye of God — at the center of Creation — so must Man's home, Earth, be at the center of the universe."

At the time of his story's setting, 1534, however, the book hadn't been published, yet its theory was already spreading like gossip, and a young Parisian theology student, Amaury Faverges, is deployed by his flinty Catholic superiors to hunt this heresy among a growing group of Lutherans. Copernicus' view, in fact, so alarms the Catholic Church that it is decided that Copernicus must be silenced, even if it requires his death.

Amaury is pulled from his studies at the College de Montaigu in Paris — a school known as "the very cleft between the buttocks of Mother Theology" — after his friend Giles, another student, is murdered. Giles, who had been spying on the Lutherans, leaves a strange message for Amaury: a crude diagram of circles that will one day change humanity's understanding of its place in the natural world.

Though Amaury would hunt the murderer just to avenge his friend, his superiors dangle something else to get his cooperation: the promise that one day poor student Amaury Faverges would be known as Amaury de Savoie; his illegitimate birth would be erased, and he would be officially recognized as a son of the Duke of Savoy. Goldstone reminds us that such an offer of legitimacy was a powerful enticement for someone living in an age when one's name and birth determined everything.

Amaury is conspicuously expelled, keeps a letter to his father condemning the Catholic Church (and which any Lutheran spy can easily find) and settles into a loud, drunken existence in a boardinghouse in Saint-Antoine, Paris' Lutheran section. Soon he is accepted among the Lutherans and, as he acquaints himself with these heretics and hunts for clues about his friend's murderer, Amaury becomes entangled with a beautiful prostitute committed to the Lutheran cause, Vivienne. Along with the mysteries of Giles' death and the strange diagram, then, Amaury faces a more familiar mystery as his desire for Vivienne grows: "To love. To be able to love. Oh, Lord, what must that be like?"

Like "The Anatomy of Deception," a Sherlock Holmesian tale that Sarah Weinman reviewed for The Times and praised for its research, Goldstone's "The Astronomer" shows us, in a story told with great care and depth, a world that, though separated from us by 400 years, feels not so different from our own.

Goldstone's story shares so much in common with Umberto Eco's "The Name of the Rose" — cloisters and theology, the focus upon learning in a place of grim, sadistic superiors and menacing plots — that it wouldn't have surprised me if Amaury had crossed paths with Eco's great hero, William of Baskerville, though their lives are separated by centuries.

The author's glimpses of 16th century daily life seem authentic, and his story doesn't wear its research heavily. Instead, it's amusing to learn a lesson in star-gazing from a Ptolemaic (Earth-centered) point of view and that bathing was a novelty (isn't washing one's hands enough?). Goldstone's portrait of life in the court of Queen Marguerite of Navarre — which is where Amaury's search sends him, accompanied by Vivienne (a couple is less suspicious than a lone traveler) — is also intriguing, as are his depictions of Rabelais, Jean Chauvin (a.k.a. John Calvin) and Copernicus, all of whom Amaury encounters.

Theirs was a world that, in an enchanting phrase by historian William Lanchester, was "lit only by fire" — and in the course of Amaury's encounters with a love from his past, surprising betrayals and unexpected brutality, Goldstone reminds us that, despite the righteousness and virtue on all sides of the struggle, there was enough selfishness and cruelty to go around. Shadows fell on everyone.

*

William Eamon also brings a distant world up close in "The Professor of Secrets: Mystery, Medicine, and Alchemy in Renaissance Italy" (National Geographic: 320 pp., $26). Eamon traces the life of Leonardo Fioravanti, a 16th century doctor in Bologna, who challenged established medical methods with a bold new way to handle illness. There were many "professors of secrets" like Fioravanti, Eamon explains, and they were called by this title because of their practice of using syrups, oils and distilled drugs "made of herbal concoctions or mineral substances" to unlock nature's secrets and battle plague, bladder stones and other ailments great and small. Fioravanti, however, is the focus of Eamon's fine study, a cocky figure who once challenged the physicians of Milan to use their treatments on 25 patients while he would treat another group of 25: "If I don't cure my patients quicker and better than they do theirs," he declared, "I'm willing to be banished forever from this city." (Eamon says it's unlikely that the contest happened but that "the historical record is mute.")

As Eamon shows, Fioravanti and other doctors like him — in combating superstition and ignorance — were seeking real medical breakthroughs that would reveal the "Magna Medicina" ("Great Medicine"). The author presents what medicine was like during the Renaissance with a wealth of unexpected details (one found, in a Renaissance pharmacy, "an alligator hanging from the ceiling" and "stuffed armadillos and miraculous healing stones") and a light, accessible touch (a discussion of blood, yellow and black bile and phlegm is found in the section "Humor me") that makes this book welcome reading not only for the summer but for any time of year.

Owchar is deputy book editor of The Times. The Siren's Call appears at http://www.latimes.com/books.