A moment later, Clark whooshes into the office. "How good of you to join us," Luthor snarks. They establish that Tess has been stashed someplace safe, much to Luthor's annoyance. He charges at Clark and sends him crashing through the office's glass doors. I was hoping for more of a Good Kira/Bad Kira flirtation, but whatever. The crash is in slow motion so that Clark's grunt sounds like a yeti in mid orgasm. Clark gets to his feet, shaken. "I guess without the darker side, you're no match for me," Luthor says. Clark whooshes away. After a moment, Luthor follows.
Next thing you know, they're zipping their way to the Fortress of Solitude. They tackle each other to the ground, then stand up and regard each other warily. "Thanks for coming," Clark says. "Not yet, but maybe later," Luthor says with a waggle of his brows. Oh, fine, that's not what he says. He realizes that Clark tricked him here by pretending to suck at fighting. When Clark tells him that their birth father is here, Luthor sneers that the Fortress is "a music box without the music." Which sort of makes it just a regular box, right? Luthor had a Fortress in his reality, but there was no Jor-El. Clark blames that on Lionel. He talks up the Fortress and Jor-El's teachings, carefully leaving out the parts where his space dad acted like a total dictatorial douche. Clark tells Luthor he can redeem himself. His proof? "You could have killed Tess in an instant, but something was holding you back." Dude, he was toying with her. Taking one's time isn't the same as hesitating.
Clark goes on: "You can go to your world and show people what you can give them, change their minds." Luthor almost instantly softens. Golly, all he was waiting for was someone to be nice to him for twenty seconds! He asks Clark why he believes in him, and Clark's all, "I know you," which, no, he doesn't. But Clark says some magical words about not being defined by his past and makes Luthor look all sad and doubtful. Clark asks for his trust, then calls out to Jor-El. A clump of crystals lights up and suddenly Clark Luthor is in the Fortress of his own reality. "Father?" he calls out. The gritty grayness of the alt-world is suddenly replaced by color and clarity. "Welcome home, my son," greets Jor-El. As the camera pans back, things seem a bit odd. The Fortress seems to be a miniature version amid much larger crystals. Did Clark trap him? Shrink him? Are we going to find out before the end of the series?