Same opening- you're a noble's son. Elise is a noble's daughter. Kids. Same shit. Laughing and merriment. Before the end of the chapter, you run into the commoner Robespierre. Guards are chasing you two, and he lies for you. That act forms a friendship. Your Father is murdered by Assassins. etc etc as they have.
You're not passive, like Ubisoft has-- the Assassins want you dead too, since obviously a son is going to avenge his Father... i.e. their entire stupid plot. But Robespierre hides you, and Elise, from the Assassins giving you chase. He saves both your asses. You've never had a commoner friend before. You're clueless to the world at large.
Then you're teenagers. The three of you are friends. Robespierre is romantically interested in Elise. You aren't. You aren't mature-- think girls are weird. After a few missions, where you help people, off Robespierre's request, you're all caught. Robespierre again takes the fall for you two. You end up saving him, from prison. Elise isn't there, to break him out. Just you. He's angry about that.
Adults. You go about your business. Robespierre gets you into the Assassin order AS A SPY, and you're all too happy to join. As you secretly dismantle the order from within- to avenge your Fathers' murder-- Robespierre gets aspirations of revolution, in France. You don't want revolution. You're a noble. You like things the way they are. Elise, though, takes a liking to his passion, about the cause. She starts spending more time with him.
The Templars recruit Robespierre. And he in turn, gets Elise to join. You're still a double-agent, working with the Assassins. You three didn't know the Templars' existed. Now, you're working alongside the enemy. Elise is more distant to you, since you're on opposite sides.
Historical Shift #1-- instead of bullshit, it's medieval with Joan of Arc, (as Elise) and Robespierre as a general-- you are fighting against them, to escape, and have to kill him. When you emerge back in Paris, that act haunts you.
Middle-game: Napoleon is an upstart lieutenant, who is your new "Robespierre-like" friend. Elise and Robespierre are now in a relationship, among the Templar order. You're staying with the Assassins not out of anything you care about, honestly, just because you'd be dead otherwise-- through prices on your head. The fact that you're in an order opposite your friends, daunts you, but Napoleon agrees with the Assassins, and its your sanity in the mid-game Especially when Elise and Robespierre consummate their relationship.
Historical Shift #2- is what Ubisoft had for the #1. You're in a romantic 1920s Paris. You have to escape from the guards Robespierre calls on you, for getting between them.
End game is using Napoleon as your agent, to uncover why Robespierre's actions are bad for France-- which in turn, increases Napoleon's power with the army (his motivation for helping you).
Historical Shift #3 - is the same Ubisoft had, about Nazi-occupied Paris, but we actually show Nazi swastikas instead of generic German iron crosses, and you're climbing the Eiffel Tower because Elise is starting to doubt Robespierre's power-mongering, and you have to save her. She dies, before you reach her- and you have a crisis of conscious, moving on.
You use your facts gathered, to plea to the Assassins, to help you stop Robespierre. In a "first" for the series, the amount of sidequests you help the Assassins with, influence their support, in your final mission. Robespierre, now mad with power, and jealous of Elise's emotional betrayal, beheads her on the guillotine. BUT, if the player completes enough favor, Elise is spared. Your final mission is Robespierre's elimination, through a variety of player decisions.
Whether or not Elise is spared, Napoleon is now a tyrant in France, because of your help, and both the Assassins and Templars want you, and Elise, dead. Napoleon feigns any notion of a friendship with you-- and the DLC is how France will deal, with your actions.
DLC (not "dead kings" are shit) is about an aged Arno, like an aged Ezio, trying to stop Napoleon's power mongering. You even help at Waterloo. At the end of the final DLC... Napoleon is resigned to Elba island, and you, and an aged Elise, live out your days-- if she died, you continue to honor her memory, as with your Fathers'.
The "Unity" in the title, comes from a difference of political option, and how you, and your companions, saw the future differently. By the last DLC, you partially accept (even your enemies') sentiments, in part, and that total, complete mindset, makes you at peace, at last.
