Ben is confused.
Ann is, among other things, not supposed to be here (she's not supposed to be here, let alone here and wearing an impossibly short skirt and smiling, her hair done up in tiny pigtail nubs). His ten-cent text from Leslie clearly indicated that there would be filthy, filthy things happening, and that those filthy things would be between him and her, the her mostly definitely not being Ann Perkins (but probably a dramatic unmasking, several items from his utility belt, and one or two wistful sighs).
He likes Ann, it's not that. She's a good person, probably one of the best people he knows, next to Leslie. And he thinks, for once, it isn't Leslie who makes Ann good, that she came that way, freshly packaged. Maybe with a bow.
"What's going on?" he finally asks, slowly, shifting his weight and looking between them -- Ann leaning carefully against the kitchen counter with a practiced air of casualness, Leslie's hand still on the door knob, attempting to press her lips into hiding a smile. After a moment of watching Leslie's tightly clamped mouth, he decides Ann is most likely to disclose the information he needs.
Entering the living room (he's been in Leslie's house before, and while it doesn't exactly thrill him that she's kind of a pack rat, it's no worse than living with Andy and April. At least Leslie is clean.), Ben strides over to Ann, ready to show her the text message that brought him over (though, if he considers it, Ann's probably already seen the message, and the three un-sent drafts Leslie typed and deleted, choosing the perfect phrasing). "No offense, but I really wasn't expecting you." He tugs at his right glove, frowning.
Ann stands up, brushes the wrinkles from her skirt and begins what Ben quickly realizes is a prepared speech, probably written by Leslie. "We apologize for the use of subterfuge in arranging this rendezvous." Okay, definitely written by Leslie. "However, we should take advantage of being so gathered and," she pauses, clears her throat and looks to Leslie for encouragement.
Leslie finally unclamps her lips and in one breath has the door slammed and her body pressed against Ben's. "Ben, please. I know the costume is really inaccurate, but it was the best Ann could do--" (Ann makes a small noise of disagreement) "--and she really wouldn't let the idea go once I mentioned it in passing. She just kept pressing and pressing and finally I was like 'Okay, Ann, but how do we get Ben to agree?' And she was like 'I know, Leslie, we should coerce him into a sexual encounter at your place, and there I will be.'"
She stares expectantly up at him, and that is most assuredly not how the exchange happened at all, but god, Leslie is adorable and Ann only looks a little uncomfortable in her get up, and Ben honestly can't think of anything else to do so he finds himself saying what he always seems to when Leslie is involved, "Why not," with a quick twist of his lips, and even as he's sort of getting used to the idea, Leslie dashes over to Ann.
"Okay, this is it, Ann," Leslie says and Ann, it what is obviously a practiced move, takes on an evil demeanor, grinning fiercely and capturing Leslie's wrists (a little too easily, if you ask Ben) behind her back and breathing against her neck (her incredibly soft neck. Ben swallows, shifts his weight.).
"You'll never escape the grasp of Harley Quinn, President Knope. You're far too valuable to this nation for me to allow you to continue your Campaign for the Betterment of All Citizens in peace!"
They've rehearsed this. The thought gets stuck in Ben's throat and slowly warms through the rest of him. It's not jealousy that flicks in increased frequency through his veins.
Leslie collapses against Ann in some approximation of a faint (far less convincing than her Emergency Stroke Face), her shirt riding up from the way she's positioned her arms. "Batman!" she shouts, a note of desperation in her voice. A note of desire there, too. Ben wonders, impossibly briefly, at his girlfriend and her girl friend, wondering at the amount of work the stars, or God, or whoever-the-fuck had to do to get them together in this room, sunset still slipping between the blinds.
He chalks it up to destiny. After all, he is the hero in this story.