Yeah, so I giffed the whole scene and I please need someone to (1) share my understanding of what happened here, and (2) scream with me about Diana:
It starts with Peter chewing out Diana
Which is right on theme with s5, and its overarching thesis for Peter, that: Neal makes you bad, watch your step with him or you won't recognize yourself, he's the apple the spoils the bunch.
Diana lets Peter's tone slide right off her, and she answers only the content, the same way she answered Hughes in Payback when he was chewing her out over letting Neal contact Keller, except with even less deference:
Peter is literally wide-eyed at her lack of apology.
But Peter rallies, and he really goes in for his second-best weapon, the kill, the legal argument.
And Diana effortlessly parries with common sense. Oh, your way? Did that yield results?
And he tries again, but she cuts him off. she won't even let him finish his moralizing, and just moves in with the very glaring flaw in his reprimand.
She explains why she couldn't let Dybek use the algorithm, and proceeds with a very clear explanation of why she has no moral ambiguity over what she's done.
And then he goes with the last, most powerful arrow in his quiver: trust me.
And Diana goes in with hers: No. I trust me.
The first half of the season was about "making peace with what Neal's done" and the second half of the season was tainted by all that vitriol between them, and then Diana slides in for the penultimate episode with "that's so fucking dumb, I did it and I am at peace with it. Think through the alternative ffs."
She has this clarity of vision that Peter has been struggling with all season, and she will voice to Peter when he's being wrong, and not in a I'm sorry but or you're right but kind of way, just flat out—you're wrong. I won't even let you finish your insipid argument.
And in standing up to Peter now, I do think she's protecting Neal from any blowback, which is honestly just hot of her. She's set up to take his side in this, without making it explicitly about Neal and what he did for Peter. It makes me wonder how the early episodes of the season would have played out if Diana had been there.