Looking for a fic

[ksai]

Okay, here's one, challenge rank 9 for lack of surrounding detail:

Harry Potter fic. There's a scene where Harry's in a car with a friendly Muggle adult, a lawyer. Prompted by him, Harry gives him a single pound note as a "retainer" to invoke lawyer-client confidentiality on some matter.

That's it. I'm completely at a loss for the surrounding plot; all I remember is that scene.

Thanks!
-- Bob

Is that one of those Fics that involve a Goblin/Wizard partnered law firm called Gripsack and Twist?