About this book:

The death of master cartographer Domenico Aureli leaves his daughter, Lena, in a precarious position. In an era where maritime charts are guarded as strategic state secrets, Lena inherits a workshop full of debt and a mysterious, unfinished survey of the southern coastline. To protect her legacy, she must navigate the cutthroat politics of the 14th-century Mediterranean, facing a temporary license from a skeptical Mariners' Guild and the aggressive rivalry of the prestigious Majorcan school.

Lena secures the patronage of the powerful Lord Valenti, who is obsessed with finding a "third channel" through the treacherous sandbars of the Serpent’s Tail—a route that would allow his fleet to bypass heavy Genoese tariffs. Assisted by her apprentice Chiara and the seasoned pilot Ferraro, Lena conducts dangerous expeditions to measure the shifting silt and currents. She discovers not only the hidden deep-water channel but also a secluded bay, realizing that her father’s obsession was rooted in a genuine geometric anomaly that has been hidden for centuries.

The conflict escalates when a rival cartographer, Antoni Beltrán, uses stolen drafts and political influence to accuse Lena of scientific fraud. After surviving a devastating fire in her storehouse and a public trial at the Guild, Lena proves the accuracy of her work through irrefutable triangulation data and ancient navigational marks. She eventually produces two versions of her work: a public chart that establishes her professional authority and a private, highly detailed version that gives Valenti his commercial monopoly.

In the final chapters, Lena successfully guides Valenti’s spring fleet through the secret passages, fulfilling her contract but realizing the dangerous weight of her knowledge. As the "Cartographer’s Daughter" finally earns her own master’s seal, she receives a mysterious letter from a distant scholar named Mercator. It hints at a vast, uncharted ocean beyond the Mediterranean, signifying that her journey as an explorer and a keeper of the world’s changing lines has only just begun.