Arno and Élise went to the drop-off location for the murderer's batch of poison.
- Élise: Charming place. What do you hope to find here?
- Arno: This is where the apothecary says he delivered the poison. I'm hoping I can pick up a trail and follow it back to the source.
- Élise: Pick up a trail? Are you a bloodhound now?
- Arno: Something like that.
- Élise: Let's go.
I'll follow your lead.
- Arno: The trail ends here.
- Élise: Are you sure?
- Arno: I'm sure.
As Élise was about to draw her sword, Arno stopped her.
- Arno: No. Wait here.
- Élise: Don't be ridiculous, I'm not letting you go in there alone.
- Arno: Élise. I have to do this myself. Please.
- Élise: I understand.
Arno left to confront the murderer.
- Élise: You'd better come back to me.
Arno followed the trail to the balcony of the Sainte-Chapelle, finding a lone figure there.
- Bellec: Took you long enough, pisspot.
- Arno: Bellec?
- Bellec: Should have known it'd be you that find me. The only question is what happens now.
- Arno: You poisoned Mirabeau!
- Bellec: He poisoned us! Peace with the Templars is a fairy tale!
- Arno: And you're the only one who can "save the Brotherhood."
- Bellec: Do you think it's the first time this's happened? The first time that the Assassins have been forced to purge their leadership? The first time that the Order has been forced to build itself back up from nothing to power? No. Masyaf, Monteriggioni, the American Colonies... it's all happened before, and we've risen anew, stronger than ever. But now... We've lost our purpose, Arno. We mired ourselves in politics and revolutions. But we're not a nation. We're an army. And in an army, "making peace with the enemy" is called "treason." But no. I'm not the only one that can save the Brotherhood. We can. Together.
- Arno: Bellec... you know I can't do that.
- Bellec: That's a pity.
Bellec lunged towards Arno with his Hidden Blade. Arno blocked the attack, and the two entered into a duel.
- Arno: Bellec, please! Come back to the Council with me, we can resolve this like reasonable men!
- Bellec: Reasonable men don't treat with Templars, boy.
Arno injured Bellec, causing him to kneel in pain. As Arno lunged at him, the two entered a struggle.
- Bellec: Bah! You're a stubborn little fuck, aren't you?
- Arno: Ask anyone.
Arno kicked Bellec into a corridor to another balcony. As he struck towards Bellec, he was thrown onto the other balcony, and the two continued their duel there.
- Bellec: Never should have plucked you out of the Bastille!
Your father'd be ashamed of you!
You disappoint me, pisspot.
I taught you better than this. Get up!
Injured, Bellec knelt by the edge of the balcony. He entered into a struggle with Arno.
- Bellec: I had hopes for you! I thought you could think for yourself!
- Arno: I can, Bellec! I just don't think like you!
Arno knocked both of them over edge, and they fell onto another balcony.
- Bellec: Open your eyes, boy! I've seen Templars put entire villages to the sword, just for the chance of killing one Assassin! Tell me, in your vast experience - what have you seen?
- Arno: I've seen the Grand Master of the Templar Order take in a frightened orphan and raise him as his own son!
Bellec once again knelt in pain. After a struggle, Arno pushed both of them through the rose window of the chapel into the building. As Arno got up, Bellec disappeared. Élise then appeared outside the chapel.
- Élise: Arno!
- Arno: I'm fine. Stay there.
Arno searched for Bellec.
- Bellec: I should have left you to rot in the Bastille. Tell me, did you ever really believe in the Creed, or were you a Templar-loving traitor from the start?
- Arno: It doesn't have to be this way, Bellec!
- Bellec: You're the one who's making it so! If you'd just see sense, we could take the Brotherhood to a height we've not seen in two hundred years!
- Arno: Yes, killing everyone who disagrees with you is a brilliant way to start your rise from the ashes!
- Élise: Look out!
Bellec attempted to assassinate Arno from above, although Arno dodged the attack. Bellec then pulled out a pistol.
- Bellec: So... Now we see the heart of it. It's not Mirabeau that's poisoned your mind, it's her. She's the last piece of this god-fucked lunacy.
- Arno: Bellec....
Bellec pointed the pistol at Arno.
- Bellec: You'll thank me for this. One day.
Bellec turned to shoot Élise outside. Arno fired his Phantom Blade into Bellec's wrist, and the two continued dueling.
- Bellec: Should have listened to me, boy.
You had your chance, pisspot.
Time to end this.
Bellec would use smoke bombs and attempt to assassinate Arno from above.
- Élise: Behind you!
Defeated, Bellec fell to his knees.
- Bellec: Do it. If you've got an ounce of conviction and you're not just a love-addled milksop, you'll kill me now. Because I won't stop. I will kill her. To save the Brotherhood, I'd see Paris burn.
- Arno: I know.
- Bellec: Well fought, pisspot. Now at least have the balls to finish it.
Arno plunged his Hidden Blade into Bellec's chest, ending his life. He then saw a vision of his memories. Arno's father was engaged in a duel with a Templar, before Bellec killed the Templar from above.
- Charles: Thank you, my friend.
- Bellec: Got to get you back to that boy of yours in one piece, don't we pisspot?
Bellec gave Charles his pocketwatch.
- Bellec: You dropped this.
The vision changed to Bellec inspecting the pocketwatch while Arno slept in their cell in the Bastille.
- Bellec: Well, I'll be damned.
The vision then changed to Bellec meeting with Mirabeau at the latter's estate.
- Bellec: So you're really going through with this?
- Mirabeau: Your protégé vouches for her. Don't you trust him?
- Bellec: With my life. It's the girl I don't trust. Nothing I can say to convince you?
- Mirabeau: I'm afraid not.
Bellec discreetly poured aconite into Mirabeau's glass of wine.
- Bellec: Thought not. (Cheers).
- Mirabeau: (Cheers).
Mirabeau drank the wine and began to suffer the effects of the poison.
- Bellec: (Rest in peace).
The vision over, Arno removed his Hidden Blade from Bellec's chest, and gently laid his body on the floor.
- Arno: (Rest in peace).
Arno closed Bellec's eyes, before leaving with Élise.
Arno discovered Mirabeau's killer to be Bellec. Forced into a duel, he reluctantly killed his former mentor.
- In the cutscenes where he's fighting Bellec, Arno will always have a sword, no matter what weapon he has otherwise equipped.