Their name was only spoken in hushed tones. They were cloaked in anonymity, a legend thought to belong to the distant past.

In the early twentieth century, Barcelona basks as the center of the high-spirited Modernist movement that has captivated Western thought, art, and architecture. Yet while the city's surface is aglow with creativity, its darker underworld hides a multitude of secret societies—those that support and those that seek to undermine the architects of the city's newfound splendor.

When the death of the Grand Master of an ancient religious brotherhood seems imminent, a decision must be made as to the fate of a sacred object whose existence has been a guarded secret since the early Christian era. The Grand Master passes on the relic to a prominent member of his order, a man named Antonio Gaudí—already a celebrity in his own right. The great architect thus inherits a dual mission: to do all he can to protect the artifact from the covetous hands of those who seek to do evil and to preserve its secrecy by passing it on to a worthy person of his choosing—in this case, his young apprentice.

In honoring his pledge to forever keep the secret from dangerous hands, Gaudí hides the relic in the heart of his most precious work, in a place he believes will never be discovered.

Almost a century later, María, the granddaughter of the apprentice to whom Gaudí passed along his secret, is charged with finding the relic. But after the mysterious death of her grandfather, María doesn't know what the relic is, where it is located, or what she needs to do with it after she finds it.

With the help of her mathematician boyfriend, she begins to trace the clues that Gaudí hid in the symbolism of his sculptures, designs, and, most important, his architecture—racing against time and the evil forces aligning against her to unravel the true meaning of Gaudí's monuments and their mysterious legacy. And to finally uncover the whereabouts and importance of the sacred relic Gaudí was dedicated to protect . . .