After his fight with Superman, John Corben is locked away in Stryker's Prison, but still leads a fairly luxurious life. However, he is suffering from pains and eventually collapses. He is taken to Dr. Vale, who informs Corben that he is dying of a fatal disease but there is a "cure" of sorts. Sometime later, someone fires missiles onto the prison. Many of the prisoners attempt to escape but Superman manages to stop them. Corben, however, had been given scuba gear and manages to evade capture. He then goes to Luthor who explains that the treatment he has in mind will not only cure Corben of his disease but also make him stronger than Superman. Corben agrees on the basis that he has nothing to lose. A chunk of kryptonite and a robotic body are brought into the room. Corben awakes now feeling better than ever. A few tests reveal that he has both super strength and invulnerability. He loves having these new powers but mentions that he cannot feel anything and has no desire for food or drink. Luthor assures him that he'll be okay and sends him after Superman.
In order to get Superman's attention, Corben derails a train and waits for Superman to come. Superman shows up in short order and fights Corben to a standstill. When he notices that Superman is still stronger than him, Corben reveals his kryptonite heart. Superman instantly weakens and nearly gets killed. Lois drives up and tries to save Superman but is captured by Corben who kisses her. Corben suddenly realizes the impact losing his sense of touch, as he can't even feel pleasure. Superman takes advantage of Corben's temporary distraction and hurls him off the bridge. Later, Lois and Clark visit Stryker's Island to investigate Dr. Vale. However, Dr. Vale no longer works at the prison. Lois and Clark are still allowed to investigate his office and Clark discovers a vial containing Aroscos Retrovirus hidden within a sharps box. Lois manages to find a parking validation for LexCorp, linking Dr. Vale to Luthor. Back at LexLabs, Corben demands that he be given back his senses of touch, taste, and smell but is told that it's impossible. In rage, he rips off his artificial skin and takes on the name Metallo after the alloy he's made of and goes for revenge against Luthor. Metallo eventually finds Luthor on his private yacht and threatens to kill him. Luthor is relatively unconcerned about Metallo's anger and convinces him to leave him alive. Superman approaches the ship to confront Luthor but Metallo attacks him. It seems that Superman will die at the hands of Metallo but he manages to reveal the vial to Metallo. Superman tells Metallo that Dr. Vale was ordered by Luthor to put the virus in his food. Though Luthor tries to convince Metallo that Superman is lying, Metallo turns on him and tries to get him to drink the virus. Superman then ignites canisters of gas sending Metallo and Luthor into the ocean. Metallo can't float and sinks to the bottom of the sea. Luthor and Superman leave together.
Back on shore, Luthor gloats that Superman can't pin anything on him but Superman claims that he's not the one Luthor should worry about. It's revealed that Metallo is still functional and is walking over the ocean bed.