A Feather in sb.’s Cap 令某人引以为傲的成就、功绩或荣誉

R：Louis,I'll make a deal1 with you.
Instead of this petty charge you have against him, you get something really big
something that would chuck him in a concentration camp for years.
Be quite a feather in your cap, wouldn't it?
N：It certainly would. Germany and Vichy would be very grateful.
R：Then release him. You'll be at my place a half-hour before the plane leaves.
I'll have Laszlo come there to pick up the letters and transits
and that'll give you the criminal grounds on which to make the arrest.
You get him, and we get away.