Maybe a pitch session will help me get this out of my system.
Um. Let's see: Keith has to go to Gotham City to testify in a high-powered divorce case (the client's spouse had a business trip to Neptune, and Keith got hired to tail the cheating party while they were there). And Veronica has to tag along for some reason. Maybe she gets subpoenaed because she took the pictures and wrote up a report for Keith, or something. That'd be a cute scene: Veronica is pissed that Keith gets to go to Gotham City and she doesn't, so she tries to sell him on the idea of taking her along. Keith, being every bit as crafty as she is, shoots her every angle down, at which point she continues sorting through the mail and finds *her* subpoena, yay!
So they're in Gotham City, and hobnob a little with Keith's client, possibly meeting Bruce Wayne in passing, and then Casework Ensues. Something happens that causes the matter to go from civil to criminal, causing the DCU and Jim Gordon to take an interest. Keith and Jim wind up on the case together, and a little headbutting and a lot of mutual respect results. Babs and Veronica, not happy to be left out, meddle. They meet in civvies first, and Veronica immediately commandeers Babs as a native informant. Veronica doesn't know, of course, that Babs is also on the case as Batgirl, and it suits her purposes to track Veronica's -- and Keith's -- every move. Naturally, the various investigations cross each other's paths. As Veronica, with Babs in tow (sometimes the other way around) shoehorns her way into the case, Keith and Jim start to increasingly share each other's pain.
Also, at some point the dads have to switch daughters. For some part of the story, Babs teams up with Keith, while Veronica helps out Jim. I suspect that Keith will come out with less of an ulcer from this temporary exchange than Jim will.
Plus, Bat-action. Say, Veronica does snooping on her own, gets in trouble, and promptly gets rescued by Batgirl. I see an action scene where Batgirl scoops Veronica up in a fireman's carry and jumps out a window to avoid an explosion, then firing her jumpline to save them from becoming street pizza. This, of course, causes the oh-so-cool Veronica to freak the hell out. Maybe she wriggles free, starts to fall, and then Robin -- Dick, of course -- comes through with an assist. So you get three separate investigations: Keith-Jim, Veronica-Babs, and Batgirl-Veronica (with Robin assisting, mainly because he enjoys watching Batgirl and Veronica snark at each other). No Batman in this story; if he appears at all, it's as the airhead Bruce Wayne, whom Veronica dismisses as pretty but dumb. Maybe he offers a small assist near the end that winds up cracking the whole thing open -- purely by chance, of course, or it appears that way to Veronica.
(The denoument, of course, should be Veronica giving Keith a "World's Greatest Dad" mug. Jim has one already. Keith needs one, too.)