The villain of the piece has finally revealed himself to Misaka - not that she can do much about it, given that she's been temporarily paralyzed.
Although Aritomi isn't stupid enough to give away all of his plans to Misaka (which is surprising for a villain in itself), what is clear is that his frustration at Academy City's reliance upon espers over all else is about to boil over into an attempted revolution, with his so-called Chemicaloids of Febri and, more importantly, Janie, at the heart of whatever it is he's planning.
Leaving Misaka and Shinobu to their own devices in the assumption that they have no way of halting Aritomi and STUDY's plan (okay, so maybe he isn't so smart) allows the two of them to at least begin hatching a plan as Shinobu eventually reluctantly realises that she can't resolve this situation alone and needs help in doing so. Misaka certainly has no shortage of assistance to offer between herself, her friends and her Sisters, and with the sheer scope of this revolution at dawn becoming clear she's likely to need every last bit of help to fend off the swarm of powered suits that are all set to spearhead it.
Having complained about this particular story arc being a lot of built-up and not a whole lot of pay off previously, I should probably feel the same about this week's instalment which again was heavy with exposition and moving the show's proverbial chess pieces into place; however, a lot of the build-up this time around was pretty satisfying to watch and at least it looks like we're set for an explosive finale which will hopefully go at least some way towards justifying all of that preparation. There's no danger of this story arc even coming close to matching what came before, but I'd at least like to see the series go out with a bang.