Claiming Lex kidnapped her missing husband, Jodi Keenan threatens to blow up an underground maze with Lex inside unless he tells her where her husband is. Clark sets off to rescue Lex, but is immediately felled by the kryptonite lining the earthen walls. Trapped together, the two reveal secrets about each other that were best left unsaid. They realize the only way they will make it out alive is by helping each other.
→ see also Category:Screencaps from episode 6x19
Lionel Luthor and Lex are meeting in a series of underground tunnels. Lionel asks what Lex is doing, but Lex dodges his questions. They encounter someone welding, and when Lex asks who it is, the person takes off her mask. She says she only wants Lex and sets off a small explosion that blocks the tunnel, throwing Lionel several feet and covering him with debris. She knocks Lex out and drags him away deeper into the tunnel.
Martha and Clark arrive at the Smallville Medical Center where Lionel is being treated. He is badly injured, but he tells Clark that the tunnels are too complicated and full of debris for a rescue team to find Lex. He pleads with Clark to go find him and Clark looks conflicted.
Lex regains consciousness and the woman introduces herself as Jodi, the wife of Wes Keenan. They were both Green Berets, but she was discharged for behavior problems. She received word that her husband died in a helicopter crash, but she refuses to believe it. She produces a document case file of her husband with the LuthorCorp logo on it and demands to know what LuthorCorp is doing to her husband. She tells Lex that unless he lets her talk to Wes, she will blow the entire cave system up in 20 minutes. She starts a timer and demands that Lex call Wes. Lex finally admits that Wes is dead; he had multiple injuries from which LuthorCorp tried to save him, but he died. She is unnerved and Lex manages to get her gun away from her. It goes off and she is injured. He tells her they can still get out of there alive, but she states that the bomb is preprogrammed. Just before she succumbs to her injury, she sets off another smaller explosion.
Clark meets Chloe at the explosion site where she reports that Lionel was right about rescue efforts expected to take hours. She also states that she doesn't really care if Lex is rescued after what he did to her mother. Clark agrees, but they both know that Clark doesn't get to choose who he rescues. Clark goes to see if he can find an entrance into the caves. Just as he enters, Jodi's second explosion rocks the caves and meteor rocks fly through the walls. Clark is blown back from the blast and is knocked out.
Lana meets Martha at the hospital and pleads with the doctor to let her speak to Lionel. He relents and Lana enters. She seems concerned for Lionel until she presses into his injured hand. She demands to know why Lionel forced her into marrying Lex when he knew that Lex was orchestrating a fake pregnancy. Lionel doesn't respond until she knots his IV to make him talk. She tells him that if she killed him right now, she would be free and asks him to give her one reason not to. Lionel only says he's protecting Clark, and then he is taken into surgery. The police found a locked briefcase in Lex's car. Lana collects it and takes it back to the Luthor Mansion and shoots the locks off. She finds schematics, documents, and a disc labeled "ARES", which is a tourist video of Patagonia, Argentina. She watches in horror as a strange creature flies into the scene and kills the TV host and the camera man.
Clark recovers enough to find Lex. He says Lionel sent him to find him and they prepare to try to find a way out when Lex notices Clark's hand is covered in blood. Clark then realizes that he has a large piece of shrapnel in the back of his upper arm. Although they are both angry at each other, Lex bandages it up and admits that he is surprised that Clark is injured; he knows that when he stabbed him with a chisel, it bent. He says Clark has been hiding secrets from him since they met. Clark doesn't deny it, but he asks Lex if he's using these caves to exploit people with abilities. They argue about the breakdown of their friendship as Lex digs a hole in the wall, but meteor rocks line the narrow opening. Clark hesitates, but then attempts to crawl through. Lex winds up having to pull him through.
Chloe is on the surface of the explosion site leaving Clark a voicemail. She notices one of the rescue workers has green meteor rock dust all over his vest and goes to the mansion to find Lana. She tells her that Clark went into the tunnels and she hasn't heard from him. In a tense conversation, Lana deduces that Clark will be fine because "he's Clark Kent." She doesn't reveal what she knows about Clark, but Chloe tells her that he's not invincible and confirms what Lionel told her: Clark has a weakness. Lana admits that she has full schematics of the passageways and Chloe is shocked to realize that Lana has had access all morning and she was simply going to let Lex die.
Clark and Lex stumble through, but the tunnels all lead to dead ends. Clark finally sits down, too weak to continue. He remarks that they don't have time to backtrack because probably, no one knows about the tunnels. Lex knows he is referring to Lana and tells him that Lana is the first person he actually does trust. Clark admits that Lana told him on her wedding day that she was going to leave Lex and wants to know how Lex forced her to marry him. Lex says honestly that he had no idea if Lana would show up and says Clark can believe whatever he wants. Clark wonders if they were ever really friends. Just then the ceiling collapses, covering Clark in debris. He asks Lex to help him out and Lex looks conflicted. Lex turns and runs and Clark calls out after him. Clark summons all his strength to try and extricate himself, but is surprised to see Lex has returned with a large pipe to help him out. The tunnels are set to explode in less than 15 seconds as Lex helps Clark to a hatch exposed by the cave-ins. They frantically climb their way up; when Lex loses his footing, Clark pulls him to safety. Just as the tunnels explode, Clark and Lex make it to the surface. As Clark lies in the sun, his powers are restored.
Chloe and Lana make it to the site just as Lex and Clark emerge. Lana sees Clark's bandaged arm and touches it. They share a silent, tender moment before Lana realizes that Lex is watching them and leaves to embrace him.
Lana returns to see Lionel in the hospital. She demands that Lionel explain how threatening to kill Clark is protecting him. Lionel says that Lana's love for Clark is the only thing he could use to keep her near Lex so Clark would be out of harm's way. She wants to know what Lex is doing that is harming Clark and wonders what Martha would think about Lionel's threat, but he doesn't answer.
Chloe and Clark are still at the scene and Clark reports that all the tunnels lead to Reeves Dam. They wonder what Lex was willing to die to protect. Clark asks Chloe how she knew to come out there and she tells him that Lana knew where the tunnels were. Clark takes this to mean that Lana really is in love with Lex, but Chloe tells Clark that Lana only revealed the location when she told her that he was in danger, too.
Lex is back at home and Lana gives him the briefcase. Lex asks her if she did indeed meet Clark on their wedding day, but Lana claims that she only wanted to talk to someone to express her doubts. Convincingly, she says she knew there was something wrong with the baby, but because she thought Lex had their whole lives planned as parents, she didn't want to lie to him and pretend that everything was fine. She pointedly says that if someone lied to her like that, they would lose her love forever. Lex's face is unreadable at Lana's double-meanings.
Martha meets Clark in his loft, where he is studying the tunnel schematics, which look as if Lex was simply building a water-purification system. Martha asks him what happened and Clark admits that when Lex saved him, he recognized him for the friend he was. Martha says that after all that has happened, Clark has to let go of what their relationship used to be. Clark asks her why she stands by Lionel, but Martha says she doesn't trust Lex because she doesn't think people can change who they are. Clark wonders if what Lex has become is because Clark gave up on him.
Lex visits a facility where it is revealed that Wes Keenan is indeed alive and being held as a test subject. Wes is referred to as "the prototype."
- Tom Welling as Clark Kent
- Kristin Kreuk as Lana Lang
- Michael Rosenbaum as Lex Luthor
- Erica Durance as Lois Lane (credit only)
- Allison Mack as Chloe Sullivan
- John Glover as Lionel Luthor
- Annette O'Toole as Martha Kent
- Richard Keats as Dr. Connor
- Ben Ayers as Jason Bartlett
- Dean Redman as Fire Chief
- Michelle Brezinski as Tourist on Tape
- J. Douglas Stewart as Doctor
- Noah Beggs as Bomb Squad Leader
- Jason McKinnon as EMT
- "Tannhäuser (Overture)" - Richard Wagner
- A nemesis is an opponent or rival whom a person cannot best or overcome.
- Clark and Lex have increasingly become each other nemeses in recent years.
- Nemesis is also the Greek goddess of divine retribution and vengeance. Lana is still seeking vengeance on Lex, and was willing to let him die despite having full schematics of the tunnel passageways.
- Antagonist: Jodi Keenan
- Clarks abilities: Super-Hearing, Super-Speed, Healing factor, Super-Strength (Offscreen), X-Ray Vision (offscreen).
- Lois Lane does not appear in this episode.
- Reeves Dam is most likely a reference to the late Christopher Reeve, who played Superman in four feature films and appeared on Smallville as Virgil Swann, and to George Reeves, who played Superman in the 1950s series.
- Jodi states that she and her husband were both Green Berets, the informal name of the United States Army Special Forces Command. This operational sect of the U.S. Army trains an elite group of soldiers to specialize in unconventional warfare. 
- The classical musical piece that is playing while Lana shoots the locks off the briefcase is Tannhäuser by Richard Wagner.
- Lionel is reading A Guest of Honour by Nadine Gordimer while recovering in the hospital.
- This episode contains a deleted scene on the Season 6 DVD set. The doctor tells Martha that Lionel is critical and gives them some time alone. Martha tells a sleeping Lionel that she never would have gotten through the past year without his friendship. Lionel wakes up and is pleased to see her.
- In the past, Clark has been completely demobilized and incapacitated by kryptonite. However, he is somehow able to manage to get through the small opening in the tunnels although the tunnels had kryptonite all over.
- Lana tells the doctor at the Smallville Medical Center that if Lex dies, Lionel would be the only family member that she will have left. This is not true, because she still has her aunt Nell and her father Henry Small (through whom she has two half-siblings). However, she may have not said this to manipulate the doctor into allowing her to see Lionel.
- When threatening to blow up the tunnels, Jodi asks Lex if he's ever done anything crazy for love. Lex has indeed done something crazy for love, specifically: put seeds of discord between Clark and Lana and then hire a hypnotist to split them up. He then manipulates and brainwash Lana into believing that he is a good misunderstood man that Clark never trusted and betrayed just as he did with her too. Getting advantage of Lana's vulnerable state that he indirectly induced himself, Lex is able to manipulate her to pursue a relationship with him, he then offers Lana to live at the mansion and then pushes her to start a sexual relationship. He is able then to successfully fake a pregnancy in order to assure a positive answer to his proposal and keep her in his life.
- When Jodi said, "when you meet someone that can pull you out of the trenches, you don't just give up on them", it means something to both Lex and Jodi. First, Wes probably saved Jodi in a war they were both in, "pulling her out of the trenches" since they're both soldiers. She used "trench" here, meaning a hole underground. Second, to Lex, this is like a foreshadow, because Lex pulled Clark from the ground since he can't pass through on his own with the meteorites hanging on the wall.
- The story is very similar to the Superboy episode "Mine Games" in which Superboy and Lex are captured in the depths of the mine, and only if they work together can they leave the mine.
- Lex states that Clark was the only real friend he’s ever had but, this is not entirely true as Duncan Allenmeyer was his friend during his time at school. However, due to what happened between Lex and Duncan, Lex probably just didn’t count him as a friend anymore.
- In this episode, Clark wonders if he gave up on Lex too soon, causing him to become evil. In the Season Four episode Bound, Lex asked Clark, "Don't give up on me, yet."
- The tourist video Lana views takes place in Patagonia, Argentina, the same location that an escaped Phantom Zone wraith was seen in Zod. The landscape is also very similar.
- Reeves Dam was listed on Lex's computer in Combat as one of the 33.1 facilities that was still operational. Reeves Dam is also seen in Prototype.
- While trapped in the dam together Lex mentioned to Clark how the chisel he stabbed him with bent like it hit solid rock. This happened in Crimson.
- This episode marks the 55th appearance of Clark's red jacket & blue shirt outfit, which he wears frequently throughout the series.
- Lana gives the DVD to Lionel in a deleted scene from Prototype. The wraith is finally unleashed in Phantom where it becomes Bizarro.
- Lex: I stopped expecting you to act like a friend a long time ago.
- Clark: Were we ever really friends, Lex?
- Lex: I don't know. I have nothing to compare it to. You're the only real friend I've ever had, Clark... and somewhere along the way you saw me as your nemesis. You turned your back on me.
- Chloe: (leaving a voicemail) Hey, Clark, it's me. Again. Where are you? I feel like your stalker ex-girlfriend... even though I was never... your girlfriend... it was just an analogy, a bad one. I'm sorry, this is awkward... okay call me. Bye.
- Lex: (to Clark) Did you really think I was going to let you die alone down here, Clark? I guess you never knew me at all.
- Lionel: (to Lana) Wow. Well, I see you've embraced whole-heartedly what it means to be a Luthor.
- Clark: Mom, what if part of who Lex is is because of me? What if I gave up on him too soon?
- Martha: You'll never give up on anyone, Clark. Because your greatest strength might also be your greatest weakness: your hope.
- Clark: When Lex pulled me out of that rubble, I saw a glimpse of something I hadn't seen in years... my friend.
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