Clark (Tom Welling) goes into hiding after he discovers a startling new power that quickly gets out of control and accidentally harms Lana (Kristin Kreuk). However, after a hot new teacher (guest star Krista Allen) uses kryptonite-enhanced pheromones to convince Lex (Michael Rosenbaum) to marry her, then spellbinds Jonathan (John Schneider), Clark must get a grip on his new power in time to keep Jonathan from killing Lex.

Sam Jones III, Allison Mack and Annette O'Toole also star. James Marshall directed the episode written by Mark Verheiden.

Freak of the Week: Desiree Atkins (Krista Allen) is the new biology teacher. A heat wave has come over Smallville and everyone is feeling hot already, but when Desiree walks into the classroom, all jaws drop! To make matters worse, the first lesson is spent watching a sex ed video! Clark Kent (Tom Welling) can't stop staring at her, and she notices. He is constantly sweating, and then, his eyes start burning, and before he knows it, heat vision is coming out of his eyes, and he sets the projection screen on fire. The students are evacuated, and Lex Luthor (Michael Rosenbaum) arrives and runs up to Desiree and kisses her. He introduces her to a stunned Clark and Pete Ross (Sam Jones III) as his fiancée. He then gives Clark a wedding invitation for that night, and asks him to be his best man. Clark is shocked but accepts, saying he is honored.
Back at the Luthor mansion, Desiree is looking over the pre-nuptial agreement that Lex wants her to sign. He explains that his father Lionel Luthor (John Glover) could disown him if he didn't get her to sign it. She understands, and says she will as soon as he kisses her. He goes to kiss her, and a purple haze emanates from her mouth and into his. They kiss, and suddenly, he is spellbound into agreeing to tear up the pre-nup, stating he plans to spend the rest of his life with her.
Clark returns home and tells his parents, Jonathan (John Schneider) and Martha Kent (Annette O'Toole) about the fire incident at school. They ask him to explain, and when they hear that he was watching a sex ed video, they figure that this new ability is triggered by hormones. They advise him to stay at home until he can figure it out, but he shows them Lex's wedding invitation.
The wedding goes successfully, and, at the reception, Clark admits to Lex that he is a little shell-shocked by the speed of the wedding. He is confused that, one minute Lex is off on a two-week business trip, and the next, he's engaged. Lex explains that, the first night he met her, he knew she was different and not after his name or his fortune. He says, "You can waste your time playing it safe or you can go for it. At some point, Clark, you just know when something's right". At which point, Clark sees Lana Lang (Kristin Kreuk) and wonders.
After the reception, Clark and Lana go to The Talon for an iced coffee. They complain about the heat. They discuss Lex's sudden wedding, and she says she finds it romantic that he acted on his passion and wonders if they could ever do the same. Clark starts sweating even more, and his eyes start burning again. He tries to keep his eyes closed to stop the heat vision but can't control it, and he sets the coffee machine on fire. He freaks out and keeps moving his eyes everywhere, setting fire to everything he looks at. He manages to stop and protect Lana. Frustrated and worried, he tells his father about the incident. His father understands that he needs to master this new ability. Jonathan takes Clark out the field, and gets him to practice on a scarecrow. He tells him to remember the emotion he felt at the time in The Talon. Clark thinks of Lana and sets a fire to the scarecrow. He practices all day, and soon learns to control his heat vision. He proudly announces to his parents that he can even use it now without having to think about sex.
Desiree visits Clark in his barn. She comes onto him. She says she saw him staring at her in class, and that she is attracted to younger guys. She goes to kiss him, and the purple haze emanates. However, it doesn't effect him, and Clark manages to pull away from her. She pretends to be ashamed and runs off.
Chloe Sullivan (Allison Mack) is researching Desiree, and finds that she was called Alison Sanders and lived in Smallville. Clark tells her about Desiree coming to the barn, and explains he feels she has a hold on Lex. He decides to go tell Lex what happened, but when he gets there, Lex tells him he knows that Clark is the one that came onto Desiree. Clark tries to explain what really happened, and even shows Lex that she is actually called Alison. While he admits he didn't know that, he tells Clark how disappointed he is and asks him to leave. Desiree walks in, and Lex asks her about her real name. She admits it. She kisses him, transfers the haze and he drops the topic without asking anymore questions.
Lex shows up at The Talon and tells Lana that he is invoking the buyout clause of their partnership agreement and gives her 24 hours to vacate The Talon. He is extremely harsh, and accuses her of entertaining guests after hours and causing the fire. She tells Clark about this, and he sees her in the school hallways, and tells her he is onto her. She tells him that she influenced Lex into selling The Talon just to prove a point to Clark. She tells him that she can get Lex to do anything she wants.
Later, Desiree blows up her own car. She then accuses Clark of setting the fire onto her car, and Sheriff Ethan (Michael Kosterman) shows up at the Kents and arrests Clark. Jonathan promises to figure this out. He goes to confront Desiree at the Luthor Mansion, and finds her nearly naked, swimming in the pool. She tells him that she thinks Clark has a problem, that he is troubled, that he causes the fires and then takes credit for putting them out. She seduces him, and spellbinds him with her haze. She tells him she needs a favor from him.
Lex meets Martha at The Talon, and she tells him that she always supported him, and even went against the opinion of her husband. In the same way, she tells him that he needs to know when to disagree with his wife. She tells him, that, deep inside, he knows that Clark wasn't the one who set those fires.
Chloe and Lana visit Clark in jail. They tell him that they've dug up Desiree's history. When she was young, she dated a guy and was with him in the car by the lake when the meteors hit. The next day, the guy went crazy and killed her parents, and she inherited everything. Later, she married a shipping executive, and then got one of her students to kill him to inherit his money. It is the typical black widow scenario. She then spent all her money and set her sights on Lex. Clark doesn't buy it at first, but Chloe explains that, since she was in the throws of passion when the meteors hit, it must have enhanced her pheromone level, and can get guys to do anything she wants. Clark realizes he needs to get out of jail, because he knows his father has gone to see Desiree. The girls leave, and Clark sets a fire off in his cell. Sheriff Ethan gets him out of the cell, and Clark runs away.
Lex confronts Desiree, telling her that he feels he is loosing his sense of reason regarding business and friends. She tells him that it is too late, that the papers have been finalized and that everything he owns is hers. He tells her that she would only inherit it if he died, and then he asks her if she is planning on killing him. She walks towards the door and says no, but that Jonathan is, as she opens the door, Jonathan is standing there with a shotgun pointed at Lex. Lex tries to talk Jonathan down, and Clark shows up in time to burn the bullet that Jonathan has just fired at Lex. Desiree manages to run off. Later, Lex makes a statement that clears Clark. Lex also files for an annulment. He also apologizes to Lana with flowers, a new coffee machine and a re-written agreement to avoid this situation in the future.

Character Development: Lana is working on a video letter to send to Whitney Fordman (Eric Johnson). She gets everyone to leave a message. When Lana and Clark are alone at The Talon, she admits that she does miss Whitney but that she is still unsure about her feelings. They agree that long-distance relationships are very tough. Clark tells Lana that Whitney cares for her so much and even asked Clark to look after her while Whitney was away.
This episode starts as the first day of school after the summer. When Chloe shows up, Clark is relieved that she did not move to Metropolis after all. She explains that her father decided to take another job in Smallville with LuthorCorp, and that she is back from her internship at the Daily Planet. He still feels some tension between them. At Lex's reception, he asks Chloe if everything is ok with them, and she explains that she had let her feelings get the better of her, but that now, everything is ok, since they have agreed to stay friends and she is happy with that. Clark is happy too, but it is obvious Chloe wants more.
Before Lex decides to close The Talon, Chloe and Lana share a moment together, where Lana tells Chloe that she knows that Clark cares deeply for Chloe, but Chloe responds that Clark cares even more for Lana. Chloe admits she still has feelings for Clark. Both girls make a pact to not let Clark come in between their friendship.
Once Desiree is out of the way, Lex comes to visit Clark and tells him that he regrets having acted on his passion. He tells Clark that he probably should have taken a page out of Clark's book with regards to the way he is with Lana. Clark says that he is willing to wait for her to figure out her feelings for Whitney. Lex tells him not to wait too long.
Lana grills Clark on the incidents. She realizes that he was the only one immuned to Desiree's powers. He jokes and says that she wasn't his type. Lana then asks him about the fire in his cell, and about the fact that he was at the scene of all three fires. He gets away with it by smiling and invoking the coincidence excuse. She says it is all part of the mystery that is Clark Kent. She tells Clark that she has decided to stop putting on a brace face on the camera for Whitney and she will tell him exactly how she feels. She says she feels that relationships based on secrets and lies are doomed to fail, "don't you think so Clark?" she asks. "Absolutely", he responds. So much left unsaid in the conversation, Clark walks away.
The last scene, we see Lana recording her video, telling Whitney "We promised we'd be honest with each other, and the truth is..." and well are left drooling for more!!!