Arno accompanied his father Charles Dorian on a business trip to Versailles. While waiting in a corridor, he was distracted by a young girl. Arno approached Olivier inside the de la Serre estate. After failing to deliver the urgent message to François de la Serre, Arno returned home.

Framed for the murder of François de la Serre, Arno was imprisoned in the Bastille. Having matched the floral symbol on the medallion with the window of the Sainte-Chapelle, Arno went there to find and obtain information from Pierre Bellec.

Arno rendezvoused with Pierre Bellec on a rooftop near the Conciergerie for his last exercise before becoming a fully-fledged Assassin. Tasked with assassinating Charles Gabriel Sivert, Arno met with Pierre Bellec on a rooftop near the Notre-Dame. Abstergo initiated a server sweep, forcing the Helix initiate to evade and escape from one Helix server to another.

With Sivert dead, Arno set out to locate his accomplice, the Roi des Thunes. Arno set out to assassinate the Roi des Thunes.

The Assassin Council tasked Arno with investigating the silversmith, François-Thomas Germain. Arno made his way to the Halle aux Blés to figure out what Chrétien Lafrenière was planning. Arno arrived at the Cimetière des Innocents to assassinate Chrétien Lafrenière, the man he believed to be responsible for François de la Serre's death.

Having assassinated Lafrenière, Arno returned to an unwitting Assassin Council. Having learned of a planned ambush on Élise, Arno rushed to save her.

Arno met with Élise de la Serre at the Café Théâtre. Having discovered that François-Thomas Germain was behind the murder of François de la Serre, Arno met with Élise at Mirabeau's estate. Arno and Élise went to the drop-off location for the murderer's batch of poison. Abstergo initiated a server sweep, forcing the Helix initiate to evade and escape from one Helix server to another.

Arno met with the Assassin Council for his next assignment. Arno met with Napoleon Bonaparte to learn of Frédéric Rouille's location.

Arno met with Élise at le Marais. Arno met with Élise at Luxembourg Palace, preparing to assassinate Marie Lévesque. Following his assassination of Marie Lévesque, Arno met with Élise to escape.

Seeking to find and kill Louis-Michel le Peletier, Arno and Élise met with the Marquis de Sade at the Louvre. Having learned that Germain would be present at King Louis' execution, Arno met with Élise near the Place de la Révolution, intending to assassinate him.

Following the execution of Louis XVI, Arno returned to the Assassin hideout. While Élise secured transport to Paris, Arno set out to rid Versailles of Aloys la Touche's terror over the town.

Élise de la Serre and Arno drove back to Paris, seeking to find Germain through Maximilien de Robespierre at the Festival of the Supreme Being. After having discredited Robespierre, Arno met with Élise, who had news of the situation's development.

Having learned that Germain was hiding at the Temple, Arno and Élise sought to end him once and for all.

Ridden with grief after Élise de la Serre's death, Arno sought refuge in Franciade. There, he entered a tavern to meet with the Marquis de Sade.

Arno entered the tavern again. Having found the two patents, Arno met with Léon to study them along with the third.

With the correct keyhole revealed, Arno only needed the key to the temple door. Arno entered the temple to retrieve the artifact.