The town is evacuated on graduation day in preparation for an impending meteor shower, and Jor-El warns Clark that the entire planet is in danger if the three sacred stones aren't reunited.
Season 4, Episode 21
A teen (Steven Grayhm) who has the power to turn people into stone wants to stay in high school forever, so he keeps students captive in a fake school that's built to look like Smallville High. Elsewhere, Genevieve and Jason threaten to kill Lex if Lionel doesn't give up the sacred stone.
Season 4, Episode 20
Lana and Clark take care of a baby they find in a crater and are shocked when he ages seven years right in front of their eyes. They then turn to Lex for help, hoping LuthorCorp labs can find a way to curtail the child's growth. Elsewhere, Genevieve confronts Lionel about the missing sacred stone.
Season 4, Episode 19
Clark's entire memory ends up getting erased when he confronts a thief who has a kryptonite-based ability to wipe out people's short-term memories. As Clark learns about his life, he's shocked to discover that he has superpowers.
Season 4, Episode 18
On the night before the prom, a popular student crashes her car into a kryptonite-filled ravine and her spirit ends up taking over other people's bodies. Elsewhere, the body of Dr. Swann's assistant, Bridgette Crosby, is found in a shallow grave on Lex's property, and Jason accuses Lex of killing her. Lifehouse performs at the dance.
Season 4, Episode 17
A kryptonite-based explosion at the Luthorcorp lab creates an evil clone of Lex, and the sinister twin tries to prevent the process from being reversed by taking drastic measures, which include imprisoning Lex in the basement of his own mansion.
Season 4, Episode 16
Lois's younger sister, Lucy (Peyton List), arrives in town, and Clark learns that she has a shady past when he catches her stealing money from the Talon's register. Also, the ancient stone is taken from Lana's apartment, and Jason suspects Lionel.
Season 4, Episode 15
The day after Dr. Swann dies, Clark receives a note from the professor leading him to a message from Jor-El that instructs him to find two sacred stones. Meanwhile, Jason and Lex are in China on a related mission; and Lana learns that the witch Isobel has been trying to find the stones by using her as a vessel.
Season 4, Episode 14
Clark takes in a dog with superpowers after Lois accidentally hits the pooch with her car. While looking for its owner, he discovers the dog was part of a LuthorCorp experiment and was being used to commit crimes. Elsewhere, Genevieve (Jane Seymour) is revealed to be the person who helped free Lionel from prison.
Season 4, Episode 13
Lois is arrested for severely injuring a Metropolis University football player who harassed her. Meanwhile, Clark visits the school on a recruiting trip and discovers scandalous activity involving the team; Jason takes Lex up on his job offer, which entails spying on Lana and Genevieve. Geoff: Chris Carmack. Lois: Erica Durance.
Season 4, Episode 12
Lana is attacked at her apartment and Alicia (Sarah Carter) is the prime suspect. Clark believes she's innocent, but later has to accept that she may be guilty when the culprit attacks Jason and leaves one of Alicia's scarves behind. Genevieve: Jane Seymour.
Season 4, Episode 11
A teen (Sarah Carter) with teleportation abilities who was obsessed with Clark is released from the Belle Reve asylum and tracks him down. Though apparently reformed, she manipulates Clark's feelings for her using red kryptonite. Meanwhile, Lionel tries to convince Lex that he's a changed man; and Lana confronts Jason about the breakup.
Season 4, Episode 10
The town's residents are infected by a toxin that causes unconsciousness and horrific nightmares when the LuthorCorp plant loses control of the dangerous substance. Meanwhile, Lionel's conviction is overturned, but he feels he deserves to stay in prison.
Season 4, Episode 9
Lana meets Jason's mom (Jane Seymour) and is surprised to discover that she looks like a woman from a dream she had about Isobel, the 17th-century witch who possessed her. Elsewhere, Lex is the prime suspect in a murder case after he wakes up next to the body of a slain woman.
Season 4, Episode 8
Lana, Lois and Chloe are possessed by the spirits of witches who were burned at the stake in the 17th century. Later, the girls crash a surprise party for Chloe at the Kent farm and use a spell to turn the event into a raucous affair. Making matters worse, a Princeton recruiter visits Clark the night of the party.
Season 4, Episode 7
Clark accidentally injures another player when foreign-exchange student Mikail Mxyzptlk (Trent Ford) uses a form of telepathy to make him trip during a big game. As a result, Jonathan wants Clark to quit the team before he hurts anyone else, and Jason suspects Clark is using steroids.
Clark switches bodies with Lionel after Clark interferes with the exchange of a Kryptonian stone that was meant for an unsuspecting Lex. Consequently, Clark takes Lionel's place in prison, while Lionel takes advantage of his newfound freedom---and superhuman abilities. Bridgette: Margot Kidder.
Season 4, Episode 5
After a boy (Kyle Gallner) with superhuman speed saves Jonathan---and steals his wallet---Clark tracks him down and discovers he's a homeless kid who uses his powers to commit petty crimes. Also, Lex acquires an ancient manuscript with Kryptonian symbols, and Clark learns that it contains a mysterious map; Jason (Jensen Ackles) discovers Lana's tattoo.
Season 4, Episode 4
When two cheerleaders develop a love potion that arouses feelings of extreme devotion and jealousy, it causes a football player to attack Jason for "checking out" his girlfriend and prompts Chloe to hit on Clark. Also: Clark is made starting quarterback, a promotion that doesn't sit well with his new teammates; and Lex donates new uniforms to the team, but Clark is put off by the gesture, which he takes as an attempt to buy back his friendship. Jason: Jensen Ackles. Lois: Erica Durance.
Season 4, Episode 3
Clark tries out for football again and learns that Jason is the new assistant coach---but Clark doesn't know Jason is also Lana's boyfriend. Meanwhile, a student gets a bizarre makeover with a dangerous side effect that gives her the power to alter the way others see themselves; Lois enrolls at Smallville High for a semester after she finds out she's a few credits shy of graduating; and Martha takes a managing job at the Talon. Jason: Jensen Ackles. Abigail: Brianna Lynn Brown.
Season 4, Episode 2
Lois (Erica Durance) and Clark go to the safe house to investigate Chloe's death and end up running from military men. Later, Lois returns to her cousin's grave and discovers her casket is empty, but she has little time to react before she's attacked by an unusual being. Gen. Lane: Michael Ironside.
Season 4, Episode 1
Lois Lane (Erica Durance) arrives in town to investigate her cousin Chloe's death and discovers an amnesiac Clark in a cornfield after she veers off the road during a storm. Lois takes him to the hospital and meets Martha, who's busy keeping watch over a severely injured Jonathan. Elsewhere, Lana finds a new beau (Jensen Ackles) in Paris; Clark discovers a new superpower; and Lex needs blood treatments to help keep him alive. Bridgette Crosby: Margot Kidder.