Davis Bloome / Doomsday
10 episodes of Smallville carry this thread, 10h in all — 2 of them are in The Essentials.
Arc membership is derived from each episode's own summary text, gated to the seasons the sources place each arc in. It shows where a thread is foregrounded, not every episode it touches.
In airing order
Clark starts his new job at the Daily Planet, where he is partnered with Lois for a story on a bus explosion. Meanwhile, paramedic Davis Bloome is attracted to Chloe.
Clark suspects a recent murder at a theater may be the work of a meteor-infected serial killer, and he demands that Chloe give him names of people she's counseling at the Isis Foundation. A fearful Davis thinks he's the killer and confides in Chloe.
Brainiac slowly takes over Chloe's mind until the only person she remembers is Davis. In an effort to save her, Clark rebuilds the Fortress of Solitude in order to seek help from Jor-El.
Chloe has concerns that Davis will try to stop her wedding. Instead, the ceremony comes under attack by Doomsday, who tries to kidnap the bride. In the melee, Clark and Lois grow closer. Meanwhile, Oliver is off hunting for Lex in Cuba, where he is surprised to find Lana.
Doomsday kidnaps Chloe, and Clark searches for her while battling the Persuader with a little help from three superheroes known as the Legion: Rokk, Imra and Garth.
Tess tries to manipulate Clark into revealing his powers by staging a midair plane accident as they fly to New York for a press conference. Meanwhile, Davis learns how to control his inner beast.
Tess reveals Davis' childhood with the Luthors when she turns to Clark for help after she fails to kill Davis. Meanwhile, Davis seeks Chloe's assistance.
Clark discovers Davis is alive and confronts Chloe about her role in hiding him. Meanwhile, Oliver and Jimmy are attacked by Davis at Chloe's apartment.
Unable to control Davis, Chloe asks Clark to kill him. Seizing the opportunity, Tess gathers Plastique and a crew of meteor freaks to track down Davis, all the while planning a double cross. Things go awry, however, when Tess' true plans are discovered.
Oliver takes the lead when Clark exhibits resistance to killing Doomsday, and Chloe finds herself caught in the middle of the situation. Meanwhile, a fight between Lois and Tess takes a surprising turn.