Warning: spoilers lie ahead for the Season 3 premiere of Supergirl, called "Girl of Steel."
Supergirl has finally returned to The CW for Season 3 after the Season 2 finale that saw one of the good guys banished from Earth and the introduction of a character destined to become a big bad. "Girl of Steel" revealed that Kara is still reeling from Mon-El being forced away from Earth due to the lead in the atmosphere, and she was far from her sunny self in "Girl of Steel." In fact, for the majority of the episode, the only time we saw her content was in her dreams when she reunited with Mon-El and her mom. The villains of the week certainly didn't help her feel any better as they targeted the unveiling ceremony of a statue of Supergirl, and a lot of lives were in danger... including those of the new villain Reign and her daughter.
While other superhero shows might have simply used the incident to kill off Reign's daughter as a motivation for Reign to swear revenge on the Girl of Steel, Supergirl went a more unexpected route. Reign -- a.k.a. Samantha the single mom -- did indeed watch her daughter go down hard and be pinned by a heavy beam, and Supergirl was nowhere to be seen to help. Then, Samantha yanked on the beam with all her strength and was shocked to discover that she could lift it and crumple the steel between her fingertips. No dead daughter, no predictable motivation.
Samantha's reaction after she pulled her daughter from the wreckage made it clear she had no inkling that she had superstrength. Samantha evidently has no idea that she hails from Krypton and has superpowers on Earth. By the end of the episode, we learned of a bizarre connection between the new big bad and Kara.
Discovering superpowers on Earth is not the bizarre connection between Reign and Supergirl. Rather, the connection was revealed at the very end of the episode, with another dream sequence featuring Alura kicked off, although this dream came to a gruesome end when Alura's face became monstrous. At first, it seemed that we were watching another one of Kara's dreams... until Samantha very suddenly woke up in bed. Apparently she too has dreams of Kara's mother, which raises a very big question: why are Kara and Samantha dreaming similar dreams of the same woman?
On the one hand, the similar dreams seem to hint that Kara and Samantha are both daughters of Alura, and Supergirl technically is overdue for a secret child plot by the CW superhero standard, which introduced secret kids in both Arrow and The Flash in their second seasons. Even Legends of Tomorrow kinda sorta featured a secret kid in its second season. Maybe Supergirl is catching up.
On the other (more serious) hand, it's difficult to see how Alura could have had another child that Kara didn't know about. The future Reign was a baby when she was sent away from Krypton on the verge of destruction, and Kara was old enough that she was tasked with protecting her baby cousin. She would have definitely noticed if her mom was pregnant a year or so before she was sent away. Even if they share a maternal figure, Kara and Samantha are probably not biological sisters.
There's also the point that Alura died when Samantha was a baby, which means that either Alura was such a major presence in her early life that she left an imprint on Samantha into her adulthood or Samantha somehow had access to a recording of Alura, just as Kara has for the past couple of seasons. Given that Samantha is actually Reign and Reign is a genetically engineered Kryptonian weapon known as a Worldkiller, the odds are that Alura had a role in her very early life. The Worldkillers of DC Comics lore were created in part by Supergirl's father; Supergirl could tweak the story to have both of Supergirl's parents involved, or replace Zor-El with Alura as a contributor to the Worldkiller project.
We'll have to wait and see. Whatever the reason for Kara and Samantha's shared connection to Alura, we can say for sure that they already have a different dynamic as opponents than any on featured on Supergirl before. You can catch new episodes of Supergirl on Mondays at 8 p.m. ET, and our fall TV guide can point you toward all the other dates you could possibly need.