STORY PT. 1 – PLOT SUMMARY (SPOILER WARNING)
The story in Assassin's Creed III focuses on the ongoing struggle between Templars and Assassins (who are an ancient order of warriors whose origin trace to the first crusade; not to be confused with "assassin" in the sense of them being hitmen). The story focuses specifically on Desmond, a modern day member of the Assassin brotherhood who must protect the world from being destroyed by a massive solar flare on December 21st, 2012 (Yes, that is the day the Mayan Calendar ends. They've been planning ACIII's release to coincide with the end of the world ever since 2007.)
Desmond, holding a "Piece of Eden"
In order to save the world, Desmond and his team of three fellow assassins, including computer whiz Rebecca, historian Shaun and Desmond's dad, William, need to find a key created by an 80,000 year old "first civilization". This civilization disappeared during an event similar to the one due in December. Desmond uses the Animus, a device which lets you experience the memories of your ancestors, to look for the key by reliving the lives of other people in his bloodline who have come into contact with it. You'll spend the vast majority of the game in the animus, and this is where the real focus of the game is. In the Animus, you play as Ratohnhaké:ton (pronounced Ra-doon-ha-Gay-doo), a Native American Mohawk who, for most of the game, is referred to by the name Connor. We'll do the same because I imagine most of you don't know Iroquois, and will be pronouncing it "Ratno-something".
Connor doesn't enter into the story until the game's second act however, which will take you roughly a couple of hours to reach. Initially, you'll play as Haytham Kenway, a British ancestor to Desmond who travels to Boston after stealing the very key Desmond is after. He assembles a small band of companions in America and focuses his efforts in finding an ancient vault left by the first civilization (as it happens, this vault is where Desmond and the others are during the present). After he fails to gain access to the vault, it is revealed that Kenway is not an assassin, as one would initially have been inclined to think, but rather, he is a Templar, and you've spent the game thusfar helping the bad guys.
A young Connor gazes across the frontier
Kenway establishes a permanent chapter of the Templars in America in order to combat the Assassin order, which already has a solid foothold on the new world. However, before doing this, he has a short lived romance with a Mohawk woman. She becomes pregnant and nine months later, Connor is born. The story jumps five years into the future at which point the Templars visit Connor's village and burn it to the ground, killing Connor's mother in the process. The story jumps another nine years forward. A now 14 year old Connor is shown a first civilization relic, which tells him he must join the assassins so that he can one day come into contact with the key, which will show Desmond what happened to it, and hopefully, how to retrieve it. Connor leaves his village and visits a man named Achilles, the former leader of the Assassin brotherhood. He spends years training with Achilles, and when he is seventeen, during the fifth act of the game, you finally get to don the assassin robes you've seen in all the trailers and posters.
Connor ventures out in the world to seek revenge against the Templars and kill it's leaders, including Connor's father and the original group you helped assemble during the beginning of the game. Along the way, he encounters several historical figures from the American revolution and takes part in many of the events leading up to, and following the declaration of independence.