Venice 2009 – against the unique backdrop of Venice and its traditions Logan, a Canadian student with a great love and talent for technology, discovers the nascent world of bitcoin. Interweaving his life with that of other students, he creates a secret as precious as it is dangerous.

Venice 2023 – following what seems to be a simple burglary, the young Italian-South Korean criminologist Soo-Min, in Italy on an internship with the Carabinieri, finds herself involved in an intricate, gripping investigation conducted against a backdrop of bloody score-settling, dangerous chases and mysterious musical scores, all encapsulated within the unique setting of the Venetian islands and canals and, of course, the famous aperitifs for which the city is renowned.

Florence, 2013 – Alfredo Martelli, technical account manager and football coach, is introduced to the fledgling world of bitcoin by his nephew Gabriele, a visionary computer nerd with little desire to study. Alfred comes to share a precious but deadly secret with the players he coaches.

Florence, 2023 – Soo-Min, a young South Korean-Italian criminologist, is doing an operational, practical internship with the Carabinieri. She becomes involved, along with Yong-Soo, her mathematician friend, in an action-packed investigation, full of twists and turns, in which family and sporting values are pitted against human greed.

This is Soo-Min’s second investigation working alongside the Carabinieri. The first, set in Venice, was narrated in The Last Refrain.

Verona, 52 BC – At the height of the Gallic Wars, Gaius Julius Caesar is making final preparations for the siege of Alesia against Vercingetorix. He has to send key secret military information to his lieutenants in Verona and manages to do so thanks to the knowledge and insight of a young mathematician in his retinue.

Verona, 2023 AD – Kyaeng Jin-Woo, a South Korean tycoon, has organized a touring exhibition of priceless ancient theatre masks. The first stop is Italy, at a castle nestling in lush vineyards in the province of Verona. However, something goes awry and the most valuable mask is stolen by means of a mathematical technique which has been known for centuries. It falls to Soo-Min and Yong-Soo, who have just opened their own private investigation agency, to uncover the truth by ploughing through restoration techniques, gourmet food and family mysteries.

Hidden Signs is the third novel featuring Choi Soo-Min, a young Italian-South Korean criminologist with two operational internships with the Italian Carabinieri under her belt, the first in Venice (recounted in The Last Refrain) and the second in Florence (recounted in Team Code). Each novel addresses a different issue in Mathematics in a pleasantly informative manner. Hidden Signs is devoted to steganography, the branch of Mathematics that deals with hiding information.

Paris, 1644 – In the peace of an old French abbey, the monk Marin Mersenne devotes his days to prayer, gardening and the study of Mathematics. Four centuries later, a method bearing his name will endanger the entire planet.

Tampa (Florida), 2023 – The South Korean multinational Daeworx Technologies, whose global commissions range from satellites to nuclear power plants, is purchasing a small US company that has developed a new chip for the rapid generation of random numbers, such numbers being of crucial importance for data and telecommunications security. Someone, however, has decided to play a dangerous double game and it will be up to Soo-Min and her mathematician partner Yong-Soo, in an investigation involving trips to the Caribbean, ambivalent executives and emotional infidelity, to get to the bottom of the scheme and prevent compromised chips from reaching the market and jeopardizing the security of IT infrastructures all over the world.

This is the first international case for the young criminologist Soo-Min and her partner Yong-Soo and the fourth case in the series, following The Last Refrain, Team Code, and Hidden Signs.