For a proper dose of Ed undercover on a mission, let me recommend "Travelling Incognito" by roseveare. Let the prologue draw you in --
"What are we going to do, brother? They won't acknowledge the authority of the State or your silver watch! That place is defended like a fortress! And I don't think they're just going to let us in."-- but don't be fooled: this more of a character piece than an action-adventure 'fic (though the author gives us a sweet crowning fight sequence), as we watch Ed through the eyes of a nicely-developed, forty-something OC who almost sees him clearly. Gen, rated PG-13 for language, and a good read.
"...Brother? I don't like when you get that look on your face. What are you thinking?"
"We'd waste weeks going back to Central to tell them about this. That's weeks where we could've been getting your real body back. Besides, I don't much like the idea of returning with our tails between our legs because we couldn't complete this lame assignment. There's only one way I can think of, Al, to get inside that place."
"You'll have to sell me."
"Hey, and that means we'll make some extra cash, too. What a great plan!"