A sexy new teacher uses the power of pheromones to convince Lex to marry her; Clark loses control over an alarming new power.

Who is Desiree Atkins? The hot new biology teacher (guest-star Krista Allen) is as steamy as Smallville’s current heat wave. Desiree uses her kiss and the power of pheromones to cast her spell over nearly any man she wants.

What’s up with Lex? After meeting Desiree only a week ago, Lex plans an immediate wedding with Clark as best man. Desiree uses her pheromone power to avoid signing the Luthor pre-nuptial agreement.

What’s up with Clark? On the first day of biology class with Ms. Atkins, Clark discovers a new power as he’s "hot for teacher," a burning glance that can set objects ablaze. The first fire he unintentionally starts is the film screen in class. Clark tells mom and dad about his new ability. Later at the Talon with Lana, Clark begins to feel aroused, and his "hot" gaze burns the cappuccino machine and wall. Jonathan sets up a scarecrow at the farm, so Clark can practice, understand, and learn to control his new abilities. Desiree visits Clark in his loft, trying to seduce him. Clark refuses her, reminding her that Lex is his best friend.

What’s up with Lex? Obviously under his new wife’s influence, Lex turns against Clark due to Desiree’s lies of Clark’s advances. Next Lex tells Lana he’s taking back the building that houses the Talon and her aunt’s flower shop.

What’s up with Chloe? Upset that Clark didn’t keep in touch all summer, Chloe admits to herself and Lana that she still has feelings for Clark, but knows Lana has always been his focus. Chloe helps Clark dig into Desiree’s past. Chloe and Lana discover that the meteors enhanced Desiree’s pheromones. She is a "black widow," using her powers to marry wealthy men, then influencing other men to kill her husbands. Lex is her latest target.

What’s up with Lana? She is shooting a video to send to Whitney overseas in the Marines. She admits to Clark that she misses Whitney, but it was unwise of them to leave their relationship as they did when Whitney left.

How it ends: Desiree blows up her car, blaming the explosion on Clark. Police take Clark into custody, linking him to three unexplained fires. Martha confronts Lex at the Talon about Clark’s innocence. Jonathan tries to reason with Desiree at the Luthor mansion. Instead, Desiree uses her pheromone powers to persuade Jonathan to kill Lex. Clark escapes jail, using his abilities to start a fire and evacuate the building. Clark rushes to the Luthor mansion, finding Jonathan, under Desiree’s powers, shooting at Lex with a rifle. Clark focuses the heat of his gaze on the speeding bullet, melting it in mid-air. Desiree sets Lex’s back on fire. Clark uses his gaze to heat the door handle, preventing Desiree’s escape, then smothers the flames on Lex’s back, saving him.

Later, when Lex and Clark talk about romance, Desiree, and the power she held over Lex, Clark admits to Lex that he can wait for Lana to settle her feelings with Whitney.

Alone as she finishes the videotaped message to Whitney, into the video camera Lana says, "We promised we’d be honest with each other, and the truth is…" (we’re left to guess what she said next).