Dr. Mark Muir, a young American metallurgist, persuades American tycoon JP Morgan to hire him for the biggest shipping project the world has ever seen: RMS Titanic, at the Harland & Wolff shipyard, in Belfast. The shipyard's visionary Chairman takes the young scientist under his wing, introducing him to Belfast's Protestant elite. Mark quickly catches the eye of the charming, albeit spoilt, daughter of a magnate: Kitty Carlton. But he is also intrigued by a very different woman; Sofia Silvestri, an immigrant's daughter. Belfast, seen through Mark's eyes, is a city ridden with divisions of class and religion, from which, as a stranger, Mark should be far removed. But we soon discover that Mark is a man with a past mysteriously connected to the Catholic suburbs of Belfast.

Dr. Mark Muir's real name is Marcas Malone, and he is the son of a Belfast Catholic dockworker, Sean. Sean is an old drunkard, broken by a life of unimaginable harshness. His only remaining pride lies in Mark. Now, Sean is worried that if Mark's identity were to be disclosed, he would lose his job at the Protestant - managed shipyard. But Mark is careful and guarded. He starts finding out things about the steel used that lead him into conflict with chief designer Thomas Andrews. In the meantime, social tension escalates. A prominent figure in the labor movement, Jim Larkin, is organizing the workers in Belfast. While Kitty Carlton seduces Mark with her elegant charms, Sofia gets more involved in her fight for freedom, which she interprets in a personal way, turning down her father's apprentice, Andrea Valle, much to her father's grief.

The accident has created a terrible workload. Tensions between classes escalate. Pirrie and Michael finally manage to come to an understanding that appease the workers, but not magnate Charles Stokes. Unfortunately, Conor MacCann, Emily's younger brother, is driven towards more extremist acts after he gets fired. The Fenian movement, a Catholic terrorist group, takes Conor in. Mark suggests building a double hull for the Titanic. But Pirrie is unimpressed. It would mean wasting too much time. To try and forget his many concerns, Mark manages to take Sofia away for a romantic weekend. It is a time when love flourishes, giving both of them the illusion that everything will be fine. Henry Carlton has discovered Mark's real identity. Carlton is furious that his daughter, Kitty, has been in a relationship with a Catholic impostor. Kitty is disowned and she decides to leave Belfast. As soon as Mark comes back he is summoned and fired.

The high staked General Elections are drawing closer. The magnates have their own candidate, the Unionist extremist Albert Hatton. The fact that Pirrie does not support Hatton makes him an enemy of the ruling class. Michael is campaigning for Labour. His sister Emily helps him. But she gets arrested for giving out leaflets. This is a political measure, and Emily is only the scapegoat. On the ship front, Mark's proposition to erect higher bulkheads to defend Titanic is crushed by Ismay, the Chairman of White Star Lines, the company Titanic is being built for. When the elections occur, Albert Hatton wins a handsome majority. The third candidate, Michael, only gets a very small number of votes. Protestant and anti Home Rule extremists fume with rage and hatred, and Michael is assaulted, cruelly beaten and forced from Belfast. His brother Conor has become a terrorist and has taken lives.

The Admiralty has opened an inquiry into the Olympic accident, and Pirrie, Andrews, Morgan and Mark are invited to London. Mark is pleased to see his old friend Kitty, who has become a star. At the inquiry, the First Lord of the Admiralty, Winston Churchill, suggests that the yard could serve several ends in case of military escalation. Joanna Yaeger, Mark's old friend from New York, and Morgan's protégée, is forced into a very dangerous position: a spy. With her unparalleled access she can prove to be extremely useful to the Austro Hungarian and German causes. Back in Belfast, Mark faces a new crisis. Andrea, Sofia's old fiancée, has seen her with him and has told Pietro. Sofia is forced to choose. Sofia stays Mark. Finally he agrees to follow Sofia: they will move to London, together. He will leave Harland & Wolff and all hopes to ever find his own daughter. In a breathtaking ceremony, the Titanic is finally launched.