There has been so much information revealed about the bathtub incident in the '90s that it would be shocking (and silly) if it was unrelated to the revenge plot. Almost anyone could be the third killer, and to be fair, there could be more than three people in on it, but everything points to a trio. In the latest episode, we learn that there are not one but two bathtub babies, so one theory is that Boone is the baby boy and one of the current Kappas is the baby girl. Gigi took care of them, and now that they're grown, she is helping them carry out revenge on the sorority. Gigi does say that the revenge plot has been years in the making, so the pieces all fit. We also just found out that Grace's mom (supposedly) dies in a drunk driving accident, but it's possible that she might not be dead and that she's actually the third killer. The only thing we're really sure of is that more blood will be shed before we get the truth.
