In the fourth season of the thrilling reinterpretation of the Superman legend, these 22 episodes include the quest for three powerful Kryptonian crystals and Clark's bold attempt to keep those mysterious stones from destroying Earth. In addition to Lois Lane (Erica Durance), new characters (The Flash, Krypto, Mxyzptlk) and a new power emerge as Clark awakens to a destiny that only he can accept.
Clark (Tom Welling) returns to Smallville re-programmed as Kal-El. Intent on fulfilling his destiny, Kal-El takes to the skies to steal a powerful kryptonite crystal. Determined to save her son, Martha (Annette O'Toole) turns to Dr. Swann's emissary, Bridgette Crosby (Margot Kidder, Superman), and learns about a surprising new form of kryptonite. Meanwhile, Lois Lane (Erica Durance) comes to town to investigate the murder of her cousin Chloe (Allison Mack). Also, Lana (Kristin Kreuk) returns from Paris with a new attitude and a new boyfriend (Jensen Ackles, Dark Angel), Jonathan (John Schneider) lies in a coma, and Lionel (John Glover) faces a grim new life in prison.
Clark (Tom Welling) and Lois Lane (Erica Durance) investigate Chloe's (Allison Mack) apparent murder, but are stopped by an army officer, General Sam Lane (guest star Michael Ironside), who turns out to be Lois' father. Lois suspects that Sam knows more about Chloe's death than he will admit, and Clark discovers that Sam has recently been in contact with Lex (Michael Rosembaum). Jason (Jensen Ackles) arrives from Paris and convinces Lana (Kristin Kreuk) to continue their relationship. Suspecting that Chloe is still alive, Lionel (John Glover) sends an assassin with the power to morph his limbs into metallic weapons to keep Chloe from testifying against him.
Clark (Tom Welling) faces a surprising new foe in the form of a shy high school girl (guest star Brianna Lynn Brown) who turns to plastic surgery to enhance her looks and boost her popularity. However, things go awry when she discovers that her kryptonite - enhanced beauty causes harm to anyone she kisses - and she decides her next victim will be Lana (Kristin Kreuk). Meanwhile, Jason (Jensen Ackles) and Lana continue to hide their relationship from Clark.
Clark (Tom Welling) joins the football team at school and is immediately given the starting quarterback position after the old quarterback starts a fight with new coach Jason (Jensen Ackles). Curious about the behavior change in his old teammate, Clark and Lois (Erica Durance) investigate and discover that the cheerleaders are poisoning the teams' water with kryptonite, turning the players into Stepford-like boyfriends.
After Jonathan's (John Schneider) wallet is stolen, Clark (Tom Welling) super-speeds after the thief (guest star Kyle Gallner) but is stunned when he cannot catch him. The thief, Bart, a.k.a. The Flash, later shows up at the farm and tries to talk Clark into leaving Smallville for a life on the road together, flexing their super powers. Meanwhile, Lex (Michael Rosenbaum) buys a priceless framed manuscript with Kryptonian symbols and Clark learns that it contains a mysterious hidden map. However, when Bart steals the manuscript from Lex, he inadvertently puts Clark's life in danger and must make the decision whether to save Clark or himself.
Clark (Tom Welling) hears a painful ringing sound in his ears and is drawn to the prison where Lionel (John Glover) is being held. When he sees Lionel attempt to stab Lex (Michael Rosenbaum) with a strange glowing stone, Clark grabs for the stone causing the two men to switch bodies. Learning his new body has super powers, Lionel immediately begins wreaking havoc on Smallville. Trapped behind bars without his powers, Clark must figure out a way to get his body and powers back in order to save his friends and family.
Chloe (Allison Mack) is drawn into an underground gambling ring at school run by foreign exchange student Mikail Mxyzptlk (guest star Trent Ford) and loses her savings on a football game after Mxyzptlk uses his powers to control all the players - including Clark (Tom Welling). When Chloe discovers Mxyzptlk's secret, he kidnaps her and threatens to kill her unless Clark throws the championship game. Meanwhile, Lex (Michael Rosenbaum) threatens Mxyzptlk with deportation unless he uses his powers for Lex's benefit.
After Lana (Kristin Kreuk) reads from a spell book written in the 1600s, she, Lois (Erica Durance) and Chloe (Allison Mack) become possessed by witches that had been burned at the stake. The three witches have come back seek revenge and search for the powerful Kryptonian crystals, wreaking havoc on the town in the process. Clark (Tom Welling) attempts to stop the witches but they strip him of his powers and force him to reveal the location of the crystal he hid in the cave.
After Lex (Michael Rosenbaum) is accused of killing a young woman, Clark (Tom Welling) sets out to prove his innocence and turns to an unlikely source for help - Lionel (John Glover). Swearing he is a changed man, Lionel offers Clark insight into the crime but he asks for something in return. Meanwhile, Lana (Kristin Kreuk) meets Jason's (Jensen Ackles) parents and has a vivid flashback of the incident in Paris, leading her to suspect that Jason's mother (guest star Jane Seymour) was there when she got her tattoo.
Lex's (Michael Rosenbaum) secret experiment at Luthorcorp goes awry and causes a dangerous toxin to be released into Smallville. Those infected by the toxin, including Clark (Tom Welling), Lana (Kristin Kreuk), Lex, and Jason (Jensen Ackles) imagine their greatest fears come true and then fall into a coma. Desperate to find a cure, Clark gives some of his blood to Lex and is stunned at what Lex does with the antidote.
Claiming to be cured, Alicia (guest star Sarah Carter) is released from Belle Reve hospital and comes to Smallville to rekindle her relationship with Clark (Tom Welling). Initially skeptical of Alicia, Clark finds himself enjoying a relationship with someone who knows his secret, but when she pushes for more he hesitiates, causing her to use red kryptonite on him. "Bad Clark" emerges and whisks Alicia off to get married in Las Vegas. Meanwhile, Lana (Kristin Kreuk) decides to have sex with Jason (Jensen Ackles) in order to win him back.
Clark (Tom Welling) has big concerns after his new g-friend, Alicia (guest star Sarah Carter) becomes the prime suspect in a brutal attack against Lana (Kristin Kreuk) and Jason (Jensen Ackles). Clark initially defends Alicia, but when the evidence begins to pile up he is forced to take a hard truthful look at the situation. Hurt by Clark's actions, Alicia forces Clark to unknowingly reveal his powers in front of Chloe (Allison Mack). Meanwhile, Jason's mother (guest star Jane Seymour) returns to town with an offer for Lex (Michael Rosenbaum).
In an effort to recruit Clark (Tom Welling) for their football team, Met U sends their star player Geoff (guest star Chris Carmack, (The OC) to show Clark the perks of attending Met U. However, after one of Met U's players dies under mysterious circumstances and Lois (Erica Durance) is arrested for his murder, Clark discovers that Geoff has super powers and is using them to paralyze anyone who gets in his way, including Lois. Meanwhile, Chloe (Allison Mack) continues to watch Clark to learn more about his secret.
While driving, Lois (Erica Durance) accidentally hits a dog and she brings it back to the farm to heal. Clark (Tom Welling) realizes this is no ordinary dog after the pup lifts up a car to retrieve a ball. Clark and Lois learn the dog is a product of an aborted LuthorCorp experiment and is being used to commit crimes, but when Lois is kidnapped by the robbers and Clark is weakened by kryptonite, it is up to the dog to save them. Meanwhile, Lana (Kristin Kreuk) questions Jason's (Jensen Ackles) involvement in his mother's (guest star Jane Seymour) schemes.
After learning that Jason (Jensen Ackles) and Lex (Michael Rosenbaum) are in China searching for one of the mysterious kryptonian crystals, Clark (Tom Welling) and Lana (Kristin Kreuk) follow in the hopes of finding it first. Clark finds an artifact that leads them to the crystal but he must battle Isobel, the witch, who has once again inhabited Lana's body in order to take the crystal for herself. Meanwhile, Lex has more information on the crystals than he is letting on.
Lois' (Erica Durance) younger sister, Lucy (guest star Peyton List), with whom Lois doesn't get along, comes to town and charms everyone she meets. However, Clark (Tom Welling) discovers a darker side to Lucy after he catches her stealing money from a bar and forces her to reveal the truth about her sudden appearance in Smallville, a truth that puts Lois in grave danger. Meanwhile, the crystal disappears from Lana's (Kristin Kreuk) apartment and Jason (Jensen Ackles) accuses Lionel (John Glover) of stealing it.
A glimpse of the future Lex Luthor (Michael Rosenbaum) is revealed after a kryptonite explosion splits Lex in two and his evil side - Alexander - is released. Alexander immediately imprisons Lex in the mansion and begins his rampage by trying to kill Clark (Tom Welling) and Chloe (Allison Mack) in the lab, jousting with Lionel (John Glover) and convincing him to return to the dark side and finally, threatening to close the Talon unless Lana (Kristin Kreuk) moves in with him.
A stunned Chloe (Allison Mack) is nominated for Prom Queen and tries to talk a reluctant Clark (Tom Welling) and Lana (Kristin Kreuk) into attending the dance with her. However, after her rival Dawn (guest star), a wannabe Prom queen, crashes her car into a ravine filled with kryptonite, Dawn's spirit is released and she enters the bodies of the others making them act out of character. As a result, Lana asks Clark to be her date, Lois (Erica Durance) attends the Prom and Chloe sets the school on fire. Lex (Michael Rosenbaum) gives the seniors a special gift by having the band Lifehouse play at the dance.
Kevin (guest star), a boy who can cause people to temporarily lose their memory, turns his powers on Clark (Tom Welling) and causes him to have total amnesia. Chloe discovers what has happened and must teach Clark about his superpowers while simultaneously trying to keep him from accidentally revealing them to others. On his trip down memory lane, Clark meets Lana (Kristin Kreuk), falls in love all over again and decides to share his secret with her. Lex (Michael Rosenbaum) takes advantage of the situation and convinces Clark to show him where the three stones are hidden.
Clark (Tom Welling) and Lana (Kristin Kreuk) discover an abandoned baby in the cornfield and take him back to the Kent farm. However, once the baby ages from a newborn to a 7-year-old in a matter of days, the two realize he is aging at a rapid rate and frantically search for a cure before the disease kills him. Meanwhile, Genevieve (guest star Jane Seymour) orders Lionel (John Glover) to kill Lana or else she will send him back to prison.
Clark (Tom Welling) must stop the school photographer (guest star Steven Grayhm) after he sets up a secret simulated high school and begins kidnapping students - starting with Chloe (Allison Mack) - to keep the glory days of high school going forever. Lex (Michael Rosenbaum) and Lionel (John Glover) are kidnapped and tortured by the Teagues in an effort to find the crystal. However, after Genevieve (guest star Jane Seymour) realizes Lana (Kristin Kreuk) has it, she decides to put an end to the hunt once and for all.
Clark (Tom Welling) begins to piece together the reason he was sent to Earth after he has a nightmare that something horrible is going to happen to Smallville and heads to the cave to seek answers from Jor-El. His biological father tells him he must reunite the three crystals immediately or a disaster of epic proportions will befall the planet and even Clark won't be able to stop it. Meanwhile, Lex (Michael Rosenbaum) helps Lana (Kristin Kreuk) escape Smallville after the death of Genevieve Teague the takes shocking action to get one of the crystals away from Lionel (John Glover). Realizing they are connected to Clark, Chloe (Allison Mack) tries to stop Lex from discovering the truth about the crystals. Jason (Jensen Ackles) takes Jonathan (John Schneider) and Martha (Annette O'Toole) hostage and threatens to kill Martha unless Jonathan tells him where Clark hid the crystals.