The mystery of what happened to Jason Blossom has been the driving narrative force of Season 1 of Riverdale, with each episode doling out clues about the quarterback's murder. But the mystery of what happened to Polly Cooper is just as intriguing. What did Jason do to Polly on Riverdale? For the first few episodes of the season, we were led to believe that Jason was a womanizing jerk who used Polly and then wrecked her head, causing a breakdown that led to her incarceration in a mental hospital. But last week's episode, "Chapter Five: Heart Of Darkness," dropped a whopper of a bombshell: Jason and Polly were engaged before he was killed and she disappeared.
In our current age of rampant fan theorizing, in which TV audiences have had plenty of practice in coming up with wild predictions thanks to mind-bending shows like Mr. Robot and Westworld, pretty much every possible plot twist gets discussed well ahead of time. So it likely came as no surprise to some viewers to learn that Jason and Polly were actually in love… a theory that was discussed here immediately after the revelation about Jason's true Time Of Death in the second episode. But the confirmation that Jason didn't take advantage of Polly — that in fact the couple was a veritable Romeo & Juliet, caught between two feuding families — doesn't answer the question of what actually happened to either of them.
However, some fans have a theory: namely, that Jason got Polly pregnant. Reddit user evfishman lists the evidence for this entirely plausible scenario, including not just the fact that they got engaged so young, but also the fact that Jason was dealing drugs and selling off all his possessions — suspicious behavior for any teenager, unless he was preparing to elope and raise a child. This theory also explains why Polly has seemingly vanished into thin air; Betty's parents won't allow her to visit her sister in the hospital because she isn't in the hospital. Polly's entire breakdown was simply a cover story the Cooper parents concocted to cover the fact that they sent their pregnant daughter away to have her baby in secrecy in order to avoid the shame.
As likely as it seems that Polly Cooper was pregnant with Jason Blossom's baby, not everybody agrees with what ultimately happened to her. Some viewers ascribe more sinister motives to her disappearance; Reddit user chanjkh theorizes that Polly's breakdown was real — and was precipitated by none other than Riverdale's hero, Archie Andrews. According to this theory, on the Fourth of July (the day that she and Jason were supposed to run away together) Polly went down to the Sweetwater River to meet her fiancé after he staged his fake death via rowboat accident with his sister Cheryl. But on her way to their rendezvous, she saw a certain redheaded jock making out with Miss Grundy.
Much has been made of the fact that Archie and Jason look remarkably similar; and we learned that, prior to tutoring Archie, Miss Grundy had taken a vested interest in Jason as well. What if Polly had seen Miss Grundy and Archie together and had mistaken the teen musician for her own beloved Jason? Could the seeming sight of her baby daddy making out with his music teacher have triggered a breakdown in Polly? One big enough to lead her to break off their engagement, kidnap him… and murder him?
OK, so the idea of Polly being Jason's murderer is probably a bit of a stretch. But it seems likely that a case of mistaken identity between Archie and Jason is bound to come into play into the mystery somehow. Hopefully Betty finds her sister soon — whether she's crazy in an insane asylum or pregnant in a distant relative's house — so we can start getting some answers about what went down on that fateful Fourth of July.