Wounded to the brink of death and suffering from amnesia, Jason Bourne is rescued at sea by a fisherman. With nothing to go on but a Swiss bank account number, he starts to reconstruct his life, but finds that many people he encounters want him dead. However, Bourne realizes that he has the combat and mental skills of a world-class spy—but who does he work for?
Nine years later, Jesse travels across Europe giving readings from a book he wrote about the night he spent in Vienna with Celine. After his reading in Paris, Celine finds him, and they spend part of the day together before Jesse has to again leave for a flight. They are both in relationships now, and Jesse has a son, but as their strong feelings for each other start to return, both confess a longing for more.
A briefcase with undisclosed contents – sought by Irish terrorists and the Russian mob – makes its way into criminals' hands. An Irish liaison assembles a squad of mercenaries, or 'ronin', and gives them the thorny task of recovering the case.
