At the Luthor manor, a lawyer arrives and informs Tess that Lionel left her something in the will. She admits that she's surprised that Tess is Lionel's heir. The lawyer gives Tess a case and leaves. As Tess examines the item inside, the phone rings. It's Clark, who says they have a leak and to meet her at Cadmus labs.
Tess puts the item in her purse and goes to the ruins of Cadmus. Clark explains that Emil has gone through the files, and been unable to locate one of the clones, LX15. Supplies are still being sent there, but Tess suggests that they not consider the clone a threat. Clark believes it's evil simply because it's a Luthor. He finds a lead-lined room, but Tess insists on handling it. Clark insists that he deal with it, and goes into the room. Inside are a cot, a chessboard, supplies, and a book with a thank-you note to Tess, from Alexander. Clark realizes that Tess knew all about the clone, and accuses her of betraying him and Oliver. As they talk, Tess drops the item, a crystalline device from her purse, and Clark picks it up. He twists it, and...
...finds himself in a bedroom, naked, with two women. He dons a shirt with a stylized U version of the El symbol. Lionel Luthor comes in and says that Clark is a Luthor man, and that Clark only lives once. Clark starts to ask why he's there, but Lionel talks about how Clark has established an Ultra-Man persona to strongarm their enemies. Lionel takes Clark to the study and tosses him a rapier... and Clark cuts his hand on it. Clark wonders if it's one of Jor-El's trials, but Lionel has no idea what he's talking about and starts dueling him. Clark insists that he's not Lionel's son and swings at him, but Lionel warns him against emotional reactions and disarms him. He reminds Clark that he is his father, and he's the one who raised him. Clark plays along, and Lionel wonders what Clark would be like if a farmer had found him.
Clark superspeeds to the farm and discovers that it's up for auction. The barn is long empty, but Tess is there. She boasts that she's Lionel's bastard daughter, and starts kissing Clark. When Clark insists that he's not who she thinks he is, Tess notices that Clark doesn't have a scar on his arm and complains that Lionel used the mirror box to bring Clark from another dimension. She starts to walk away, but Clark asks for answers. She finally tells him that they are in a darker universe, and Clark Luthor is in Clark's world.
Clark goes to the Daily Planet and discovers that it has been bought out by Luthorcorp. Lois hits him in her car, and Clark tries to apologize. She knows him as her editor at the newspaper, and warns him that he won't find an excuse to get her fired. Oliver comes up and embraces Lois, and Clark realizes that they're engaged. As a reporter tries to talk to Lois, Clark says that Oliver is lucky to have Lois. Oliver is unimpressed, noting that they've known each other since boarding school and Clark has already thrown away his opportunities. Lois and Oliver leave, and Clark hears an alarm. He goes to investigate and finds a burglar trying to escape with stolen good. He corners the man, who knows who he is, and the crook explains that no one sees Ultra-Man and lives. Clark realizes that Lionel has turned him into a murderer.
Clark Luthor arrives and smiles. He goes to the Daily Planet, where Tess is trying to locate her Clark. Mistaking Clark for his counterpart, she wonders where he's been. He kisses her and she notices the scar with the L brand on it. Clark Luthor is well aware that he's in another universe, and Tess explains that Lex killed Lionel. Tess feigns interest and warns that she's watched constantly, but Clark wants the box so they can destroy it and make sure they're never returned to their own universe. Believing that Tess is his Tess and used the box to travel to This Earth as well, Clark lets her go and promises that the world won't know what hit it.
Lois is getting coffee on her afternoon off when she gets a call from Tess. She ignores it and tries to pay for the coffee on her card, but discovers that it's been declined. A bystander says that he has a call for Lois on his cell phone. It's Tess at Watchtower, who has found her using the city's CCTV. She tells Lois to get to Watchtower right away.
When Lois arrives at Watchtower, Tess is trying to contact Oliver and his team without success. As Tess starts to explain what's going on, Clark Luthor smashes in through the skylight and knocks them aside. When Lois tries to get through to him, assuming he's under the effects of red kryptonite, he knocks her out and tells Tess that he won't go back to Lionel's world. Instead, he'll conquer this world. He demands the box and she asks what happens if she doesn't. Clark Luthor informs her that he'll kill her.
Tess goes to Lionel's office and opens the hidden safe containing the Kryptonian journal with the page about the mirror box. As she seals the hidden panel, Lionel comes in and realizes that she's up to something. He's well aware that she's planning a coup against him, and takes the pages that she removed from the journal. Tess insists that she loves Clark, and Lionel admits that he's not surprised given Clark is a god among men. He wonders what Clark sees in her, and insists that he won't let Tess ruin everything he's planned for. Tess slaps him, and Lionel calls his security guards. As she's taken away, Tess asks why Lionel couldn't love her like he loved Clark, and Lionel says that she's not special enough.
At the Fortress, Clark tries to contact Jor-El. Lionel is waiting for him, having set up an office there. He explains that they took extreme measures to silence the Jor-El construct, and that he's there to check their progress. Lionel says that he has to choose between Tess and Clark, since Clark Luthor killed Lex. He informs Clark that Tess was looking for the page from the journal that describes the mirror box from Krypton. Clark claims that he told Tess to find it so he could destroy it, and just wanted to make Lionel proud of him. Lionel explains that Oliver has the mirror box, after his family received it when Veritas dissolved. Clark promises to get it from Oliver, while Lionel looks after him.
At their engagement party, Lois finds Oliver drinking by himself on the balcony. He believes that the whole world hates him, despite Lois' assurances. Oliver wonders why she chose him, and Lois assures him that he's a good man. As they start to kiss, Clark whisks Lois away at superspeed. Oliver gets a call from Clark, who say that he wants the mirror box in return for Lois.
Clark has taken Lois to the top of the former Luthorcorp building, and tries to explain that he's from an alternate world. He describes all of the personal things he knows about her, and says that she must know in her heart that he's not Clark Luthor. Clark assures her that he can't live without her love, and leaves.
At the Watchtower building, Clark texts his location to Oliver to make the exchange. Oliver denies knowing about the box, but has used an orbital satellite to confirm that Lois is okay. He seals the doors and activates a kryptonite ray generator, and then prepares to shoot the weakened Clark. Clark tries to explain, but Oliver doesn't believe him and explains that he owns most of Smallville, and mined it for kryptonite. When Clark insists that he's no threat, Oliver asks why he took Lois. He says that he believes in justice and prepares to shoot Clark, but Clark insists that he's not a murderer. However, Lionel arrives and knocks Oliver out, and then asks what his plan was to escape to another world. Clark realizes that Lionel knew he was going into a trap, and told him that Oliver had the mirror box. Lionel reveals that he has the box, and says it's time for a long overdue father/son talk. When Clark says that he's not his son, Lionel says that he made their future his whole preoccupation, and let him kill Lex, his true son. Lionel says that he's sacrificed everything for Clark, but failed him. He starts beating Clark with his belt while noting that no true Luthor would have let Lionel live.
Oliver recovers consciousness and shuts down the kryptonite generator, and Clark knocks out Lionel and takes the mirror box. He tells Oliver to be ready when Clark Luthor arrives, and that in his world they do work together. Clark activates the mirror box as Lionel runs toward him...
... and finds himself in the ruins of Watchtower, where Oliver, Tess, and Lois are ready to take him down. Clark appeals to Lois, who knows who he is.
Later, Lois checks herself out of Metropolis General and Clark comes to see her and brings flowers. He explains that he destroyed the mirror box, and admits that some part of Clark Luthor came from him. When Lois wonders how she put up the other Clark, Clark notes that she didn't. She assures Clark that he has nothing to worry about.
At the manor, Tess goes over photos of herself as a child, as well as of Alexander. Clark comes to see her and apologizes for his comment about the Luthor blood. He admits that she had good reason to worry about his reaction, and Tess says that she's upset that Lionel tossed her aside because she wasn't good enough. Clark says that she's lucky that Lionel didn't raise him, and that it's the person, not the blood, that corrupts. He apologizes to her, and Tess says that she hid Alexander because she didn't want anyone taking the closest thing to family she has away from her. She figures that Alexander will only be found when he wants to be. Clark takes her hand and assures Tess that they'll face Lex together, and that she's not alone anymore.
Somewhere in Metropolis, Lionel Luthor buys a newspaper and admits to the newsstand owner that he's back just in time.