Desmond Miles is a bartender who is kidnapped by a powerful corporation called Abstergo. While captive, Desmond is informed that he can use a machine called the Animus, created by Abstergo, to relive his ancestors' memories. He consents to use the machine, and relives the memories of his ancestor, Altaïr ibn-La'Ahad.
Altaïr, Desmond's ancestor, is a disgraced assassin because he broke the three tenets of the Assassin's Creed. These being, 1. Never kill an innocent person, 2. Always be discreet, 3. Never compromise the brotherhood. In order to regain his former status Altaïr must hunt down nine key targets. Altaïr reluctantly agrees and he slowly hunts down the men. He realizes they all have something in common. After assassinating all nine targets and discovering that his ninth target was in fact a trap, Altaïr confronts Robert, the leader of the Knights Templar, in front of King Richard I of England, leader of the Crusader army. Altaïr informs Richard that Robert is plotting to betray and kill him, which causes him to encourage a duel to the death between Altaïr and Robert. Richard then believes Altaïr. Upon dying, Robert confesses to Altaïr that there were not nine, but ten Templars conspiring to take the Piece of Eden. The tenth being Al Mualim, who wanted to keep the Piece of Eden for himself and therefore sent out Altaïr to kill the others. Back at Masyaf, the assassin's fortress, Al Mualim had taken over the minds of the people inside. Altaïr manages to defeat and kill him in a duel. The memory Abstergo was searching for, which located the Piece of Eden, reveals it is only just one of 28 that are scattered across the world.
Back in 2012, Abstergo sends a team to recover as many Pieces as possible. Deciding they do not need him anymore, they give orders to kill Desmond. Lucy Stillman, an Abstergo employee who revealed to Desmond that she is an undercover Assassin, convinces them not to kill Desmond until they recover the Pieces, buying him time. Desmond is left alone in the Animus room, and by the use of Altaïr's Eagle Vision inherited from the "Bleeding Effect" caused by the Animus, he sees many symbols drawn in blood on the wall in his room and on the floors of the lab. These symbols contain references to the end of the world in many different languages.
