After the previous episode of Durarara!! left Anri on the run from the Yellow Scarves after witnessing with her own eyes the real truth regarding their leader's identity, this latest instalment takes a bit of a step back for a while to show us this exact chain of events from Anri's perspective.
Thus, we get to see Anri's suspicions increasingly aroused regarding Kida's behaviour as it becomes more erratic, with him spending less time both with herself and Mikado. This suspicion certainly isn't helped by Izaya stoking the fires as per usual, as we see him planting information in the direction of both Anri and Mikado during the course of the episode to ensure that these particular pieces in his bizarre and dangerous game continue to move effectively under his will.
Eventually, Anri uses Saika's power to confirm what she already knows deep down - That Kida is indeed the leader of the Yellow Scarves. This traumatic mental state of affairs seems to push Anri dangerously close to allowing Saika to take control of her... indeed, it may well have already pulled her into this state despite the best efforts of Selty to help her as something of a kindred spirit when it comes to fighting both with your past and the sense of being somewhat "otherworldly". So, the bonds that previously bound Kida, Mikado and Anri together continue to do so ever more tightly, expect those bonds are rapidly beginning to represent nooses around their respective necks.
Although you could probably argue that positing so much of what we already basically knew from Anri's perspective was superfluous to requirements here, it nonetheless worked well in establishing her as a major player in what is to come, as well as drawing the lines regarding who her allies and enemies might be as we roll towards the climax of the series. Similarly, Izaya's hand can now be seen everywhere and in every decision, and it seems increasingly improbable that any one party will be able to reverse this state of affairs before its too late. All of this means that Durarara!! is getting more fascinating by the week, and I can only hope that there's enough time left within the series for a thorough and comprehensive resolution to this story arc which is warming up tremendously.