Alfred Borden has a twin, and lives the act even at home with his wife and child. He and the twin switch places often, with one portraying the others assistant Fallon. This also explains why he seems to be two different people around his wife, who kills herself. The machine that Tesla builds for Angier turns out to be a cloning machine, which transports the clone in the process. So, each night Angier uses the machine onstage, he is actually cloning himself, with the copy falling through the trap door into a water tank and drowning. Angier uses this to frame Borden for his murder. Angier takes on the name Lord Caldlow and is granted custody of Bordens daughter after the trial, so apparently, he has suceeded in taking everything from Borden as he set out to do. At this point, Angier is still unaware that Borden has a twin. One of the Borden/Fallon twins is hanged for the crime, while the other returns to shoot Angier, setting fire to his dead body and the duplicating machine. As Angier is dying he states You dont see where you are, do you?, and, as the fire burns, Borden/Fallon looks around and realizes that he is in the underground holding area for the water tanks with the dead Angier clones inside of them. We are then shown Borden/Fallon reuniting with his daughter who is with Cutter, (who knew that Borden was a twin the entire time). The movie ends with a quick shot of one of the dead clones in a water tank.
