At long last, "Riverdale" introduced Polly (Tiera Skovbye), the missing Cooper sister. Just as quickly as she appeared, though -- and with child, no less -- Polly ran away, leaving her sister Betty (Lili Reinhart) once again looking for clues to bring her home.

Figuring out what happened to Polly has been a driving force for Betty -- and learning that apparently Jason Blossom (Trevor Stines) loved her, and was planning to build a life with her, came as a true shock. But what's Betty to do, now that her sister has once again disappeared?

"For Betty to have seen her sister, and how she was stuck in this sort of dark, really lonely place, and thinking there's a chance she could save her -- only to go to the hospital at the end of the episode and see that Polly's ran away," Reinhart explains, "I think it leaves Betty pretty devastated."

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Where did Polly go, though? That's what those who tuned in -- and those living in Riverdale, for that matter -- must be wondering. It's certainly what's racing through Betty's head, which Reinhart says "wears on her emotionally." Thanks to photos from upcoming episodes, we know that the two sisters will be reunited again -- but what happens then?

Throughout the season, Betty's own parents have been lying to her about Polly's whereabouts and the reason she was sent away. Now the truth is out, and there's still a killer on the loose. The Coopers had to have known they couldn't keep Polly or her secret hidden forever, so what game are they playing?

Whatever it is, don't expect Betty to give up her investigation with Jughead (Cole Sprouse) into what exactly the town is hiding. "It's adding a piece to the puzzle, a little bit, and she's putting the pieces together," Reinhart says.

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Of course, even with her mission to figure out who killed Jason Blossom, you can't help but feel for Betty through all of this.

"To have something brought back into your life and then taken away again... You feel bad for Betty," Reinhart admits. "I certainly do, sometimes."

"Riverdale" airs Thursdays at 9 p.m. ET/PT on The CW.

Posted by:Chris E. Hayner

Chris E. Hayner is equal parts nerd, crazy person and coffee. He watches too much TV, knows more about pro wrestling than you do and remembers every single show from the TGIF lineup. You may have seen him as a pro-shark protester in "Sharknado 3." His eventual memoir will be called "You're Wrong, Here's Why..." TV words to live by: "I'm a firm believer that sometimes it's right to do the wrong thing."