In last week's episode of Superman & Lois, Superman (Tyler Hoechlin) met Morgan Edge (Adam Rayner) in the desert, a moment the villain chose to reveal his real identity: he's a Kryptonian, just like Kal-El, and he calls Superman his brother. Now, "O Mother, Where Art Thou?" picks up right where "Loyal Subjekts" left off, with Superman and Morgan Edge facing one another. The conversation between the two continues and Edge explains that his name is Tar-Ro, and he is the son of Zeta-Ro, his father, and Lara-Ro, his mother. Lara, of course, is also Superman's mother, which makes Tar-Ro and Kal-El half-brothers.
Tar-Ro reveals that before Lara married Jor-El, she was genetically matched with Zeta-Ro in some sort of arranged marriage, and through that union, he was born. But after Lara met Jor-El and fell in love with him, she divorced Zeta-Ro and married Jor-El instead. When Krypton was destroyed, Tar-Ro was sent to Earth, but he landed in the British countryside. Now, Tar-Ro intends to bring back as many Kryptonians as he can, including his mother, and bring Krypton back to greatness here on Earth. He asks Superman to join them but the Man of Steel is quick to turn him down. After a brief fight, Tar-Ro disappears, telling Superman he has some time to think about his offer.
Following the Kryptonian attack at the Kent farm in "Loyal Subjekts," Sam Lane's soldiers have now permanently set up shop around the house and throughout Smallville. Now, they know what Edge is up to, and they're determined to stop him. A clearly distraught Clark returns home to his family, where he tells Lois (Elizabeth Tulloch), Jordan (Alex Garfin) and Jonathan (Jordan Elsass) everything that happened with Edge. They all urge him to travel to the Fortress of Solitude, where he will be able to get answers about Edge's claims. Certain that his family is safe thanks to Lane and his soldiers, Superman flies to his Fortress, where he confers with the Jor-El artificial intelligence. The digital manifestation of his father confirms Edge's story, telling Clark that his mother was indeed married to Zeta-Ro before him and that she had another son. Clark is understandably angry that the A.I. kept the truth from him, but Jor-El insists that it was for the best. When Clark then asks if there's any hope of saving the people Edge has implanted with Kryptonians, Jor-El says he can't help him because the technology Edge is using, which is called the Eradicator, was invented by Lara.
At the farm, Jonathan unpacks his father's revelations and tells his brother he saw the footage of an evil Superman siding with his fellow Kryptonians and killing Lois Lane in footage from John Henry Irons' parallel Earth. He wonders if his father could ever choose to side with his brother, given that the revelation that one has family out there would be shocking to anyone. However, Lois insists that Clark would never do that, as they -- Lois, Jordan and Jonathan --- are his real family. After this discussion, Sam informs Lois that they have located Kyle Cushing.
At the Cushing house, Sarah (Inde Navarrette) snaps at Lana (Emmanuelle Chriqui) for once again trying to defend her drunk father, and she storms off. However, Lana knows that isn't the truth, and that her husband got involved with whatever it is that Edge is planning. She confronts him and asks when exactly he joined Edge's leadership program. However, they are interrupted by Lois, who comes for a visit. She exchanges a few pleasantries with Lana and Kyle, at least until the latter's Kryptonian identity takes over and attacks both women. Lois takes him down with Kryptonite, and Sam Lane's soldiers then barge in to take him into custody.
In talking with Lana, Lois and Clark learn about a man named Donovan, who is likely connected to Edge and the procedure to implant people with the identities of Kryptonians. Eventually, the army locates Donovan and, with the help of Superman, the Eradicator technology is secured. The machine and Donovan are brought to Smallville, and Donovan is asked to reverse its effects. However, he doesn't know how -- only the technology's creator would. Clark then puts the pieces together and realizes that they need to use the machine to bring his mother back into a human host. Sam doesn't believe they'll be able to find a volunteer on such short notice, but Lana Lang steps up, ready to put her life on the line to save her husband.
Lana goes into the machine, and she is successfully taken over by Lara. Clark then gets a moment he never imagined: he talks to his mother and tells her all about his life and his family. In return, a warm Lara explains that the Eradicator technology was never meant to be a weapon used for invasion and that it takes weeks before the Kryptonian consciousnesses are permanently bonded to a human host. Thanks to Lara, Superman now knows there is still time for him to save everyone and free them. But at that moment, Edge activates his dozens of Kryptonians all over Smallville, and they take to the skies, ready to invade Earth and take out the Man of Steel.
The Man of Steel flies away with the Eradicator, but he's followed by an army of Kryptonians led by Edge. Superman then turns his heat vision, as well as their own, onto the Eradicator to super-charge it and uses his own body as an energy source, creating a solar flare powerful enough to sever the connection between the device and the hosts. As a result, all of the humans who had been taken over by Kryptonian consciousnesses are freed, including Kyle.
The crisis is thankfully averted, but Superman is nowhere to be found. After using the last of his power, he reaches the Fortress of Solitude and secures the Eradicator before falling unconscious. As the episode comes to a close, the Cushing family is reunited, and Edge's army is no more. Now, only Tar-Ro and his right-hand woman Leslie remain, but he insists that they haven't lost yet.
Superman & Lois stars Tyler Hoechlin, Elizabeth Tulloch, Dylan Walsh, Alex Garfin, Jordan Elsass, Emmanuelle Chriqui, Inde Navarrette and Wolé Parks. The series airs Tuesdays at 9 p.m. ET/PT on The CW.