Ed discovers Sloth and Al at Tucker's research lab. He tries to convince Al that the Homunculus is not their mother, and not to be trusted, but Al is pretty sure that it'll be fine. So Ed has to do things his way. He reveals the pieces of his mother's inactive person that he dug up in Rizenbul, stunning Sloth, and giving him a chance to seal her forever. Lust had drawn a sealing transmutation circle with her claws, so it could not be destroyed, and Ed lured Sloth into it. The deal was almost done, when Al in his infinite wisdom decided that he was going to save the homunculus, so he threw the box containing a piece of his mother out the window, thus freeing Sloth. Lust held her at bay while Ed went to get the box, but Wrath was waiting outside, and decided to absorb the box into himself so Ed couldn't get it back. More and more it became clear that the brothers would not win this battle so easily, especially with Al helping out the Homunculus. Sloth freed herself from the circle, and while Ed chased Sloth, who was now controlling Al's body from the inside, Wrath and Lust squared off. Lust is easily destroyed though, as Wrath found her locket and used it to stop her on the transmutation circle. Wrathhuged Lust and headed off to find Sloth. Fortunately for the brothers, who were not in great shape at this point, Wrath was a bit inexperienced, and foolishly merged himself with Sloth. Having the box inside of him, this stopped them both and gave Ed his chance to destroy his creation, Sloth, once and for all.
'Humankind cannot gain anything without first giving something in return. To obtain, something of equal value must be lost. That is Alchemy's first law of Equivalent Exchange. In those days, we really believed that to be the world's one, and only, truth'.
-Alphonse Elric
Edward and Alphonse Elric are two brothers gifted with the ability of alchemy, the science of taking one thing and changing it into another. However, alchemy works on the theory of Equivalent Exchange - for something to be created, something else of equal value must be sacrificed. When their mother dies, Edward decides to do the unthinkable - bringing her back to life by breaking one of Alchemy's biggest taboos and performing Human Alchemy. Thinking they have nothing more to lose, he and Alphonse make their attempt - but something goes horribly wrong. In the process, Alphonse loses his body and Edward loses his leg. Ed manages to save Al by attaching his spirit to a suit of armor, but at the cost of his arm and leg.