Lawrence is a mathematically gifted but socially awkward young man who joins the United States Navy during World War II. Initially assigned to the military band due to his poor physical coordination, his cryptographic talents are soon recognized by higher command. He becomes a leading code-breaker in Detachment 2702, where he is tasked with hiding the fact that the Allies have cracked German ciphers.

Bobby is a capable and highly skilled Marine corporal who experiences intense combat early in the war. He relies on his strict military discipline to shield himself from the violence around him and develops a dependency on morphine following severe combat trauma at Guadalcanal. Despite his rough exterior, he is deeply observant and becomes a central operative for the secretive Detachment 2702.

Randy is a 1990s computer programmer and hacker struggling to find purpose after a disastrous business failure that cost him his savings. He travels to Southeast Asia to help launch Epiphyte Corporation, aiming to create a secure data haven in the Philippines. He often feels alienated from his academic girlfriend's social circle and prefers the clarity of code to social politics.

Enoch is a mysterious, red-bearded Catholic priest and chaplain attached to Detachment 2702 during World War II. He speaks multiple languages flawlessly and demonstrates an advanced understanding of cryptography, medicine, and human psychology. He operates through a vast network of hidden contacts and appears at crucial moments to offer guidance or medical care.

Amy is the fiercely independent daughter of Doug Shaftoe, working alongside her father in Semper Marine Services. She approaches business and relationships with a pragmatic, almost militaristic directness. She becomes increasingly involved with Randy Waterhouse and Epiphyte's operations in the Philippines as they lay underwater cables.

Goto Dengo is a Japanese soldier and mining engineer whose patriotic belief in the Japanese Imperial Army erodes as the war progresses. Assigned to construct a massive, highly classified underground bunker in the Philippines, he begins to view his mission as a moral burden and seeks a path to spiritual redemption.

Known as "the Dentist," Dr. Kepler is a wealthy, aggressive businessman and investor with a reputation for using ruthless legal tactics to acquire technology companies. He attempts to exert control over Epiphyte Corporation, employing surveillance and litigation to force Randy and Avi into compliance.

Doug is a former Marine who operates Semper Marine Services alongside his daughter Amy. Raised away from his parents due to wartime tragedies, he is a hardened maritime operator who discovers a sunken German U-boat while surveying cable routes, pulling Epiphyte into a dangerous treasure hunt.

Avi is the business visionary behind Epiphyte Corporation. Driven by his family's history in the Holocaust, he believes strongly in creating decentralized communication and financial systems to protect individuals from oppressive governments. He handles the strategic maneuvering while Randy handles the technology.

Alan Turing is a brilliant British mathematician who serves as a mentor and peer to Lawrence. Working at the secretive Bletchley Park, he designs machines to break the German Enigma ciphers and shapes the Allied cryptographic strategy, treating mathematics as both an abstract art and a crucial weapon.

Rudy is a gifted mathematician who returns to Germany and is coerced into developing cryptographic systems for the Nazi regime. Disillusioned with the Reich, he embeds hidden weaknesses and messages in his ciphers, hoping his old friends will discover them and undermine the Axis powers.

Glory is a Filipino woman who shares an intense, brief romance with Bobby Shaftoe just as the war begins. She is separated from him when Manila is attacked, eventually joining the guerrilla resistance against the Japanese occupation forces.

Charlene is an academic whose career focuses on cultural and gender theory. Her success and integration into a social circle that Randy finds alienating creates a widening rift between them.

John is a software engineer and cryptography expert recruited by Avi. He writes the sophisticated encryption code for the company's financial systems and brings a libertarian, highly secure approach to data management.

Tom is a technology specialist working for Epiphyte, tasked with stress-testing networks and presenting system security to potential investors. He harbors intensely personal secrets on his hard drive.

Beryl is the experienced CFO of Epiphyte Corporation. She provides the structural financial planning and risk assessment necessary to keep Avi and Randy's ambitious technology project grounded in business reality.

Andrew is Randy's former role-playing companion who turned a shared software project into a legal disaster. He later re-emerges online as a hostile critic of Epiphyte and eventually acts as an aggressive litigator backed by Dr. Kepler.

Colonel Chattan is a British intelligence officer managing the operations of Detachment 2702. He oversees the strategic deception campaigns designed to prevent the Axis powers from realizing their codes have been broken.

Bischoff is a highly skilled German U-boat commander. Though initially serving the Reich, he recognizes the war's impending loss and uses his submarine to transport stolen Axis wealth while conspiring with old academic friends to secure a future beyond the war.

Originally a prisoner enslaved to dig the Golgotha bunker, Wing survives the brutal conditions of the war and decades later becomes a powerful Chinese military and business figure. He aggressively pursues the hidden Japanese gold in the 1990s, using his resources to block Epiphyte's efforts.

Mary is an Australian woman of Qwghlmian descent who captures Lawrence Waterhouse's immediate and obsessive attention. Her presence entirely disrupts his previously ordered, mathematical view of the world, leading to a clumsy but sincere courtship.

Julieta is a Finnish woman who takes Bobby Shaftoe in during a lull in his military service. She provides him with a brief period of domestic peace away from the horrors of the war.