In the series finale, Tess Mercer (Cassidy Freeman) learns that the planet Apokolips is coming to destroy humanity, and that Oliver Queen (Justin Hartley) is under the possession of Darkseid.

Meanwhile, the Lionel Luthor from Earth-2 (John Glover) attempts to bring his deceased doppelgänger's son Lex (Michael Rosenbaum) back to life.

Showrunners Brian Peterson and Kelly Souders attempted to preserve the intended ending envisioned by original series developers Alfred Gough and Miles Millar several years earlier.

The episodes featured the return of several former actors, including John Schneider, Aaron Ashmore, Annette O'Toole, and Michael Rosenbaum.

Seven years in the future, Chloe Sullivan (Allison Mack) reads a comic book titled "Smallville", detailing the rise of Superman, to her son.

Flashing back seven years, Lois Lane (Erica Durance) and Clark Kent (Tom Welling) argue about their upcoming wedding.

At the Luthor Mansion, Tess Mercer (Cassidy Freeman) is confronted by Granny Goodness, who offers her one final chance to join Darkseid's forces to spare her life during the coming destruction.

Tess, awakening on a table inside a laboratory, is greeted by the parallel universe version of Lionel Luthor (John Glover) from Earth-2, who reveals that they are underneath the ruins of the Luthor Mansion, where Lex has been hiding, taking his clones' vital parts and grafting them to his body to mend himself (as revealed in the season premiere episode "Lazarus").

After overhearing a government radio broadcast containing disguised references to nuclear weapons, Lois sneaks on board Air Force One.

There, the spirit of his father, Jonathan Kent (John Schneider), presents him with the suit Martha made for him, and Clark takes to the sky, saving a crashing Air Force One, and vanquishing Darkseid by pushing Apokolips back into space.

News arrives of a bomb found in an elevator uptown, and Clark excuses himself and runs to the rooftop, ripping open his shirt and revealing his signature sigil.

This meant that they were unable to write the series finale, although Millar later noted that, in their minds, "the last moment of the show would have been him putting on the suit and flying off into his future and his destiny".

[1] According to executive producer and showrunner Kelly Souders, she and fellow executive producer and showrunner Brian Peterson kept Gough and Millar's original ending in mind when they began working on the finale, because the scenes that Gough and Millar had envisioned represented "real wish fulfillments for fans".

[3] According to Souders, the writers initially wished to include more members of the Justice League but, because of budgetary constraints, these ideas did not come to pass.

[7] Aaron Ashmore returned after his original character, "Henry" James Olson, was written out of the series during the eighth season episode "Doomsday".

[10][11] The airing of the finale was preceded by months of speculation as to whether actor Michael Rosenbaum would return to reprise his role as Lex Luthor.

[13] Before the airing of season 10 commenced, Welling argued that, for him, Luthor's return would have to be the inspiration for Clark to finally become Superman, because the idea of one character without the other was unthinkable.

[15] Had Rosenbaum not elected to return, Souders explained that Lex still would have played a part, but would have been more of "a puppeteer behind the scenes" and the fact that he was still living would have "been a reveal at the end of the show", sans the dialogue.

Kreuk stated that Peterson and Souders never approached her about being in the finale, and that she was glad that they had not, because she was fond of how Lana's story arc ended in season eight.

A fan of the series himself, he was particularly pleased with the way in which the various story arcs were wrapped up, highlighting the scenes in the Fortress of Solitude, the flash forward seven years, and the reappearance of Schneider.

[5] The suit that Clark dons in the series finale was originally used in the 2006 film Superman Returns, worn by Brandon Routh.

[23] Jeff Jensen of Entertainment Weekly's PopWatch complimented the episode, writing that "the series finale of Smallville did what it needed to do: It completed the circuit on an epic coil of story that began 10 years ago".

[27] Moody was critical that the substantial scenes in the episode were surrounded by "countless minutes of poorly paced padding, filler, and manufactured conflict", and that "the bulk of this two-hour finale was just painful to watch".

[28] He heavily criticized the show for focusing so much of the romance between Clark and Lois, and wrote that it detracted from the "better" plot concerning Darkseid and his minions.

[29] TVLine ranked the fact that Clark Kent "barely suits up" in the finale as one of "TV's 20 Biggest Disappointments of 2011", writing that "we never quite were treated to seeing the series star clad in the full costume, in flying mode", although they wrote that it was "a super-nitpick".

[25] Peterson and Souders, however, were reportedly "thrilled" by the "great debate", noting that "what [the producers] wanted to do all along was show hints at where he was going, because Clark's destiny as Superman is a whole different story that is yet to be told".

[25] Dyess-Nugent praised Rosenbaum's acting, arguing that it shook "the show awake, sending the needle hurtling rudely into the red zone".