The mystery of the Stack's House letterbox Revealed (NOT)

After three visits I have discovered the true mystery of the Stacks
House Letterbox. Does it really exist?

Visit Number One: After some extensive research we found what we
were quite certain was the right place to look. The next day we
visited it over lunch hour. There seemed innumerable good hiding
places though nothing in the clues revealed exactly where.
Surreptitiously we inspected cabinets, corners and little hiding
places. No luck. Finally we carefully asked someone there. We
remembered that the Smithsonian microbox went missing when someone
very UNdiscretely asked about it. We carefully asked someone, "Do
you know what a letterbox is?" "No. Never heard of it." We asked
if she knew an Amy. "Oh, yes she works nights." Finally we talked
to the person who might be Marcus but without saying the word
letterbox. No luck from this fishing. We decided to go home and
write the placer.

We wrote the placer who kindly responded that, "Yes you have to ask
but not those you did since they wouldn't know anything." She said
to ask someone like Marcus.

Visit Number Two: All we had to do was ask the someone like Marcus.
Great. Back we went over lunch hour again. We asked the one like
Marcus. He wasn't Marcus and he had no idea what we were talking
about, but he'd ask Amanda. Marcus would be working tonight though.
While waiting for Amanda we asked someone else, also no luck. Amanda
came over. "Hi, we are looking for the Stack House letterbox which
we understand is kept _____." "Oh, I know about that. But I don't
know where it is. I'll look for it for you." She left. And she
never returned. Having twice heard that Amy and Marcus worked at
night we ran out of time and decided to return that night.

Visit Number Three: As we sat down we heard someone saying hello to
Marcus. Great. Here is Marcus our troubles are over. "Hello Marcus
we are looking for the Stack House letterbox which we understand is
kept _____." "Oh, I know about that. It's in the office. But the
office is locked and I don't have a key." Argghhhhhhh! We spent the
next hour listening to some very good music.

So far we have actually had quite a good time on our visits because
the place is good to visit letterbox or no. But I am convinced
there is no letterbox. It must simply be a conspiracy to get you
visit. ;-)

1. Most people there don't know what we're talking about.
2. Those that sort of do say we have to speak to someone who's not
there.
3. When we return, that someone says it's locked away, we'd have to
try a different time.
4. What will it be next time? "Sorry, someone got here before you
and took it out. This is reminding me of Monty Python's "The Cheese
Shop". "Sorry, we're fresh out of that one."

Evasive? Uh huh. It doesn't exist. That's what I say. Mystery
solved!

Scarab of the Doubtful Guests