This is episode 9 of my Assassin's Creed 3 Remastered Walkthrough for the Xbox One X

Immediately after the events of the previous game, Desmond Miles, along with his father William, and allies Rebecca Crane and Shaun Hastings, find the Grand Temple of the First Civilization in a cave in New York state and access it using their Apple of Eden, an ancient artifact of immense power. After partially activating the temple, Juno uses it to communicate with Desmond. Desmond is placed in the Animus where Juno's influence causes him to experience the life of his ancestor Haytham Kenway in England, 1754.

Haytham assassinates a patron at the Royal Opera House and steals a medallion; the Key to the Temple's inner chamber. Haytham is dispatched to the American Colonies to locate the Temple. While in Boston, he kills a slave trader, freeing a group of Mohawks including a woman named Kaniehti:io, who asks Haytham to refer to her as Ziio after he proves unable to pronounce her full name. She helps Haytham find the Temple in exchange for him killing General Braddock. Haytham and Ziio find that the Key is not able to open the temple itself. The pair develop a romantic relationship during their time together, which results in a son, Ratonhnhaké:ton. Haytham is then seen inducting a new member, Charles Lee into the Order, only for it to be shown to actually be the Templar Order instead of the Assassins.
Connor becomes conflicted about eliminating the Templars, and hopes to work with Haytham towards a common vision of peace and freedom. However, Haytham remains convinced of the chaos of freedom and the necessity to control the nation by replacing Washington with Lee. Lee is disgraced by Washington for attempting to sabotage the outcome of the Battle of Monmouth and takes refuge in the heavily fortified Fort George. Connor infiltrates the fort and is confronted by Haytham; they duel, and Connor kills him. Connor later kills Lee and recovers the Key. With the Colonial Templars eliminated, Connor returns to his village only to find it empty, and the Sphere left behind. Using it, Juno instructs him to conceal the Key where it cannot be found; Connor buries the Key in the grave of Achilles' son, Connor Davenport.