2030: in a gray and hyper-controlled Milan, Diana and Luca are sent on a mission to Lugano to spy on the exchange of a powerful weapon. Not far away, Edo Zani, Manticore Italy's heir, has to respond to an unexpected proposal from the head of Manticore France, Cecile. In the flashbacks, Diana investigates her parents' suspicious passings when she meets Gabriele, a mysterious Citadel agent.

Diana and Edo form a secret agreement and make their first move, but they underestimate Cecile's fierce reaction. While Manticore Italy is under attack, Ettore Zani has to step in to stop a war from breaking out. In the flashbacks, Diana completes her training with Gabriele and becomes a Citadel agent.

Ettore sends Edo and Diana to Sicily on a sensitive mission that threatens their alliance. However, under the Mediterranean sun, the two discover they are connected by much more than their objectives. Eight years earlier, Diana infiltrates Manticore and carries out her first mission.

Diana is captured and struggles desperately to survive while Ettore has to make a hard decision in order to restore Manticore Italy's power, as memories resurface of the day when his relationship with Edo was shattered forever.

Edo leads a group of agents in an attack on the Manticore France's headquarters in Paris. Just as Diana is about to get her hands on the weapon, she is forced to decide which side she is on, as she had to do eight years earlier, the night Citadel was destroyed.

As Diana ponders her choice, Edo works on a powerful new weapon. Ettore tries to get closer to his son, playing one last, surprise card. In a flashback, the Zanis mourn Enrico while Diana realizes she's the last living Citadel agent.