Lois tries on lipstick laced with red kryptonite and becomes overwhelmed with a desire for Clark and makes her move. Clark is infected when she kisses him. As Kal, he lets his feelings and emotions be known about several recent events in his life, and makes another plea to Lana to not marry Lex.
→ see also Category:Screencaps from episode 6x13
Chloe and Clark arrive at the Talon and Clark is appalled that there is an elaborate Valentine's Day party going on. Jimmy arrives shortly afterward with Lois, who is still upset over her breakup with Oliver. Chloe realizes Jimmy brought Lois because he is trying to set her up with Clark. Jimmy and Chloe leave Lois and Clark by themselves, who realize they were set up. Clark leaves, and Lois wanders over to a vendor booth run by Star, a mystic who sells novelties such as potions and future-readings. She guesses Lois has a broken heart and gives her a lipstick, claiming that after putting it on, she will fall in love with the first man she sees. She tells her she gets the deep red hue from red meteor rocks and when Lois puts it on, she sees Clark in the mirror behind her, apparently becoming instantly smitten.
The next morning, Lois arrives at Clark's house in a leather jacket, knee-high boots and a miniskirt. She tells Clark that she's over Oliver now because she has realized she is in love with him, instead. Clark is stunned and remains speechless. She gives him a mix CD and advances onto him. Clark knows she is acting strangely and as soon as she mentions dancing and turns her back, he super speeds away.
Chloe is leaving for work and finds Lana at her door. Lana says she realizes she left things in a weird place last time they talked and says she will quit asking Chloe about Clark's secret if Chloe admits that he has one. She asks Chloe to be her Maid of Honor and Chloe agrees. Later, Lana and Lex are getting ready for their engagement dinner when Lex shows her how he has made up a room into an elaborate and ornate nursery for the baby. He wants to announce Lana's pregnancy at the dinner, but Lana is reluctant. She doesn't want everyone to think that she's only marrying Lex because she's pregnant. Lex thinks Lana is hesitating over her decision to marry him.
At the Daily Planet, Clark tells Chloe that Lois is acting strangely. She doesn't believe him until Lois herself shows up. Lois then shows Clark and Chloe a heart shaped tattoo which reads "Lois & Clark Forever" and they are both shocked. Chloe promises to look into what's causing her behavior while Lois drags Clark into a phone booth and kisses him. The red kryptonite is transferred to Clark and Kal takes over, prompting a heated makeout session in the phone booth. Kal then takes her to an empty office and Lois recognizes she has kissed him before and says that he must be the Green Arrow. Clark flippantly replies that he was just dressed as the Green Arrow so she wouldn't know it was Oliver. Lois starts talking about Oliver, but a jealous Kal boasts that he is miles ahead of him. He takes her to the roof of the building and, wanting to show off, makes a super-powered leap to Queen Tower with Lois in his arms. Lois is amazed, they break into the Queen Tower loft and make out on Oliver's couch, which is only interrupted when Kal notices an invitation to Lex and Lana's engagement dinner. He decides to crash the party.
Chloe is on her way to the party when Jimmy shows up. He has brought her flowers for Valentine's Day. He remarks that she is dragging her feet about getting to the party, but Chloe denies it. She asks him to look into whatever is causing Lois' behavior and he reasons that Lois and Clark just have great chemistry. He thinks Chloe is jealous of Lois because of her feelings for Clark. Chloe gets annoyed and says she is tired of him bringing up their relationship, telling him to back off. Chloe goes to the party and Jimmy goes to visit the mystic and asks her for the antidote. She gives him a green glowing spray.
Kal arrives at the Luthor Mansion with Lois in tow and crashes the dinner. He offers his opinion on his mother's relationship with Lionel Luthor and rudely remarks that Chloe must be happy that Lana is getting married because now maybe her years of pining for Clark might pay off. Lex tells him to leave, but Kal shouts back at him. He then finishes his tirade in front of the stunned guests by tossing Lex a rattle and toasting to Baby Luthor, insinuating that her pregnancy is the real reason Lana is marrying Lex. Lex is enraged and proceeds to attack him, but Kal easily throws him to the side. He takes Lana's arm and drags her away with him. Martha realizes that Clark must be on Red Kryptonite as Jimmy arrives with the antidote for Lois, and Martha goes after Clark. Lois appears heartbroken until Chloe and Jimmy cure her with Star's spray, removing her memories of the day's events.
Kal takes Lana to the barn and tells her that they must still be in love and she should marry him instead. Lana is upset that he embarrassed her, but she does not deny it. He forces a kiss on her and eventually she kisses him back. Lana tells him that he doesn't love her, but just can't stand to see her in love with someone else. Just then, Lex arrives and Lana runs into his arms. Kal announces that Lex has always just wanted what he had and Lana is just a trophy to Lex and Lex is nothing but her consolation prize and then Kal ask Lana to say she doesn't love him, and Lex looks at her as she doesn't deny her love. Kal asks again and walk up toward Lana, but Lex points a gun at him warning to stay away from her. Lana is scared and surprised by Lex's gesture which was extreme and inappropriate at the situation. Nevertheless Kal mocks Lex before he grabs him by the throat and starts to choke the life out of him, admitting that if he had known who Lex was destined to be, he never would have rescued him from the bridge years ago. Lana tries to pry Kal's grip off of Lex, but he was far too strong. Lex grabs a long chisel and tries to stab him with it. Kal crumbles to the ground in pain just as Martha shows up. She tells Lana to leave, but not before Lana notices the chisel on the ground, its point bent up. Martha reveals a green meteor rock as Kal writhes in pain, sweating profusely. He is restored to normal as Clark.
The next day, Clark has to face all the rude things he said and did as Kal. He says he didn't mean them, but Martha states that in fact, he says exactly what is on his mind when he is on Red K and shouldn't always bottle up his emotions. He says that he can't let Lana marry Lex, and Martha tells him he needs to let go of his feelings for her. Lois arrives at this point and it is evident that she does not remember anything about what happened yesterday when she was affected. She is obviously uncomfortable about her lack of memory, and Clark gently teases her about the affair, grinning broadly as he banters with her as usual. He doesn't tell her the whole story, but when he shows her the mix CD she made for him, and she is clearly embarrassed, and the pair exchange awkward glances.
Chloe thanks Jimmy for his help in restoring Lois. She gushes about how great they work together, but Jimmy brings up Clark's behavior. Chloe brushes him off and Jimmy gets annoyed, saying that Clark was acting like a jerk and Chloe always makes excuses for him. She tries to assure him that there's more to the story, but Jimmy gets upset and challenges her by saying if she had to choose between him and Clark, she would choose Clark. Chloe assures him that she likes him, but he doesn't believe her. He says they should take a break and leaves as Chloe starts to cry, heartbroken.
Lex gets Dr. Langston to check up on Lana and he gives her a clean bill of health. Lex indirectly mentions that Lana was kissing Clark back and Lana asks him if he was going to shoot Clark to protect her or because he wanted to hurt him. Lex admits that he felt he had a right to go after Clark. He says he doesn't know what he would do if he lost Lana, who seems to start having doubt about the goodness of Lex, who exits and meets the doctor in the hall, who remarks that Lana's pregnancy "isn't typical" but is progressing "as scheduled."
In her bedroom, Lana opens a drawer in her dressing table where she has hidden the bent chisel Lex used on Clark, setting the stage for her journey into discovering the truth about him.
- Tom Welling as Clark Kent and Kal
- Kristin Kreuk as Lana Lang
- Michael Rosenbaum as Lex Luthor
- Erica Durance as Lois Lane
- Allison Mack as Chloe Sullivan
- John Glover as Lionel Luthor (credit only)
- Annette O'Toole as Martha Kent
- Simone Bailly as Star
- Fred Henderson as Dr. Langston
- Julie Brar as Dinner Guest #1
- Noel Johansen as Dinner Guest #2
- Judith Johnson Turner as Dinner Guest #3
- Marshall Caplan as Dinner Guest #4
- Allan Gray as Dinner Guest #5
- "Our Finest Hour"- Ginger
- The color "crimson" is a purplish red to a vivid red,
- Lois' lipstick is colored Crimson. Red is also the color of the kryptonite that infects Clark in this episode.
- The title 'Crimson' is very similar to Season Two's Red, which also dealt with red kryptonite.
- Antagonist: Kal
- Clark’s Abilities: Super-Speed, Super-Strength, Invulnerability, Super-Leaping
- The CW released a poster with the tagline "The Legendary Love affair begins tonight." to promote the start of Lois and Clark's hidden romantic feelings for each other that are brought to the surface by red kryptonite.
- Interestingly, Lionel Luthor does not appear in this episode, even when it is his son's engagement party and Martha is there. In a deleted scene, Martha goes to the Mansion and gives Lana a gift, a piece of heirloom family jewelry. She explains that Lionel was out of the country and unable to return.
- According to the Smallville Official Companion Season 6 book, Annette O'Toole objected to Martha attending the party, out of loyalty to Clark. However, the writers explained that Lana thought she intended to stay after dropping off the gift, so she did in order to not hurt Lana's feelings. 
- It is interesting that Lois and Oliver were invited to the engagement party, since Lex has openly expressed disdain for both of them: Lois in Solitude and Oliver in Reunion. Lana could have invited them, but she has only met Oliver in passing and, while earlier episodes such as Oracle have portrayed her and Lois as on friendly terms, they are not close friends. Lois is not seen at the wedding.
- This is the first time that Clark, Lana, and Lex are seen in the Kent barn together.
- Even though Lois is seen putting the Whitesnake CD in the CD player at the Kent Farm as Clark zips away, Clark hands the same CD to Chloe in the next scene at the Daily Planet. However, he could just have picked it up in super speed when Lois turns her back
- Even though Star doesn't get Lois or Clark's name (onscreen) at the party, she says that she thinks Lois and Clark's destiny is more entwined than they realize when Jimmy gets the "anti-love potion".
- This is the third time that Lois learns Clark's secret. The first two times were in season 4 episodes Spell and Blank respectively.
- Lois is the first human to be infected by Red kryptonite.
- This is also the second time that Lois finds out that Oliver is the Green Arrow. Although she had her suspicions in Hydro, a plan by Oliver and Clark convinced her otherwise.
- Clark mentioned that Lex wanted everything he had, with Lana being at the top of that list. Lex had said this to Clark in Vessel right before he was inhabited by General Zod.
- Lois' reaction after using the lipstick is similar to Chloe's when she is dosed with a green kryptonite love potion in Devoted. Both gaze at Clark and murmur his name dreamily.
- Chloe saying "Why does that make me picture her wielding an axe to every man in Metropolis." This ironic due to the fact that when Chloe was possessed by Dawn Stiles in Season Four's Spirit, she does exactly that to Clark and Jonathan.
- Clark stating that "Oliver's not even in the same League as me" is a nod to them both being in the Justice League.
- Chloe giving Jimmy a bow tie is a nod to comic book's Jimmy Olsen's trademark bow tie. Although this is only his older brother, at the time it was believed this was the Jimmy found in comics.
- The way Clark demonstrates his powers to Lois is similar to the way he did it to Lana in the alternate timeline of Reckoning.
In Other Media
- Chloe gives Jimmy a bow tie for Valentine's Day, a nod to the character traditionally wearing one.
- After Clark super-leaps with Lois from the Daily Planet balcony to Oliver's balcony, Lois remarks that Clark is "Able to leap tall buildings in a single bound", which is a word-for-word quotation of one of the popular descriptions of Superman's most well-known superpowers.
- This episode is also similar to the Lois & Clark episode Pheromone, My Lovely where Lois is under a perfume which causes her to drop her romantic inhibitions,
- In this episode, the effects of red kryptonite were removed by green kryptonite exposure. A similar incident occurred in the fourth season of Lois and Clark, where Superman lost fine control of his powers due to red kryptonite exposure, and the effects only ended after he was grazed by a green kryptonite bullet.
- As in Superman IV: The Quest for Peace, Clark reveals his powers to Lois by walking off a building. In both cases, Lois forgot soon afterwards.
- It is stated for the first time that the entity that saved Clark in Static and Labyrinth is the "Martian Manhunter", a name presumably thought up by Chloe.
- After attacking Lex the night before, Martha Kent points out to Clark that red kryptonite "strips away his inhibitions." Alicia Baker said something similar to Clark in Season Four's Unsafe.
- This is the first appearance of red kryptonite since Season Four, and Lois' first encounter with Clark's Kal personality.
- Jimmy was last seen in Hydro.
- Since red kryptonite brings out Clark's inner most thoughts and desires, this episode reveals that he hates Lex, that he is still in love with Lana, has thoughts about a relationship with Chloe, is physically attracted to Lois, and is angry about Martha and Lionel's friendship.
- This is the first episode since Justice that Lois appears in where she isn't in any physical danger.
- This episode marks the 49th appearance of Clark's red jacket & blue shirt outfit, which he wears frequently throughout the series.
- The truth behind Lana's atypical pregnancy is revealed in Progeny.
- Lois eventually finds out Oliver's secret for good in Siren.
- Clark refers to "Love Potion No. 9." Love Potion No. 9 is a 1992 movie starring Sandra Bullock and Tate Donovan, and was inspired by a famous doo-wop song of the same title.
- Jimmy jokes that aphrodisiacs work like "Barry White songs", a reference to the American singer famous for his sensual soul and disco love songs.
- Clark: (to Chloe) You're the only person who can make me feel guilty, relieved, and a little sad, all in one sentence.
- Lois: Is it really wrong that I want those chubby cherubs to burst into flames?
- Chloe: What are you doing? We were supposed to take Clark out tonight, remember?
- Jimmy: Yeah, well, Lois was out alone, and then it hit me; Lois, and Clark.
- Chloe: Lois and Clark?!
- Jimmy: You got to admit, they got chemistry.
- Chloe: Yeah, so do nitroglycerin and peroxide, and I don't suggest putting them together.
- Lois: Please tell me we weren't just set up.
- Clark: Looks like it.
- Lois: Us? That's like... hot fudge and halibut.
- Clark: I take it I'm the halibut.
- Lois: Naturally.
- Clark: Well, I've had my fill of fat babies with arrows. Knock yourself out, Lois.
- Clark: Lois is... into me.
- Chloe: She's into you? What like--(Clark holds up Lois' mixed CD) Wow. She really pulled out all the stops.
- Clark: She's not herself, all right? It's like she-- overdosed on Love Potion #9 or something (Chloe giggles) and this isn't funny!
- Chloe: Oh, it's pretty funny!
- Kal: I'd like to see Oliver do this-- (Kal grabs Lois and jumps from the Daily Planet rooftop to Oliver's balcony) What did you say about a dorky farm boy?
- Lois: Able to leap tall buildings in a single bound. I can't wait to see what else you can do.
- Kal: Well I'm fast, but not too fast.
- Kal: And look. My own mother would rather raise a glass with the enemy than stand by her own son.
- Martha: Clark. You're not yourself.
- Kal: It's okay, Mom. You're more a Luthor than a Kent these days, anyway.
- Kal: (to Chloe) After all, once Lana's off the market, all those years of unrequited pining may actually pay off. Can't say I haven't thought about it.
- Kal: To baby Luthor. The real reason that Lana's marrying you.
- Jimmy: (about Lois) It's so weird to see her acting like a girl.
- Lois: I knew I'd kissed you before-- in the alley. You're Green Arrow.
- Kal: Hardly-- I was just pretending to be so you wouldn't know it was Oliver.
- Lois: Oliver? Oh my God. All those times he disappeared. What is my deal with emotionally-unavailable weekend warriors?
- Lois: Well, I guess it's better that neither of us remembers. I can't even really picture the two of us, um... you don't think that we...
- Clark: Think that we what?
- Lois: You know... that we...
- Clark: No, Lois.
- Lois: Ahh.
- Clark: I think I'd remember.
- Lois: Yeah, of course you would. Highlight of your life.
- Lex: So I have this dilemma: I can't decide between Stegosaurus or Mr. Duck.
- Chloe: Hey, put another one down for the J-Chlo team!
- Clark: Mom, you don't think I really meant those things I said about you and Chloe?
- Martha: I think there was a grain of truth in all of it. Every time you've been affected by red kryptonite, it hasn't changed who you are. It's just stripped away your inhibitions. I think you need to start being more honest about how you feel.
- Clark: So... you're saying that I want to kiss Lois and keep Chloe in my back pocket while the whole time I'm still in love with Lana?
- Martha: You're the only one who can sort that out.
- Kal: If I had known who you were going to turn out to be, I'd never would have saved you on that bridge.
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