CHAPDISC: DH12, Magic is Might

[Carol]

No: HPFGUIDX 180899

Carol earlier:
> 
> > <snip> I'm wondering how Lupin escaped being seen if the DEs were
already watching the house and he didn't have an Invisibility Cloak.
Maybe I'm forgetting something?
> 
> Potioncat:
> The first step was covered by the FC. So no one would see Lupin or 
the Trio there. I think the step is visible. Have we determined that
the house itself is invisible to the DEs? <snip>

Carol responds:

The house itself is definitely invisible:

"However, two cloaked men had appeared in the square outside number
twelve, and they remained there into the night, gazing in the
direction of the house that they could not see" (DH Am. ed. 201). I'm
sure you remember that Harry couldn't see the house, either, until he
read and processed DD's note about the HQ of the Order being at twelve
GP. Standing outside number eleven, he sees number ten to his left and
number thirteen to his right. As he thinks about number twelve, "a
battered door emerged out of nowhere between numbers eleven and
thirteen, folowed swiftly by dirty walls and grimy windows. It was as
though an extra house had inflated, pushing those on either side out
of its way" (OoP Am. ed. 39). The Muggles next door, naturally, are
oblivious, feeling and seeing nothing unusual.

So, unlike the house at Godric's Hollow, which was visible even though
the Potters inside it were not (until the Fidelius Charm was broken),
12 GP is invisible to anyone who doesn't know the secret. (It also has
the protections placed on it by Orion Black, presumably including
anti-Apparition--unless you're a House-Elf).

Since the house is invisible to Harry in OoP and to the DEs in DH, and
since it pushes the other houses aside to make room for itself when
its visible, it stands to reason that the steps--all of them--would be
invisible, too. All that the DEs can see when Harry misses his step is
his elbow sticking out of the cloak for a second as he struggles to
catch his balance. So it doesn't seem to matter whether he landed on
the first step (the closest to the door and possibly the largest) or
the last--it's the Invisibility Cloak, not the Fidelius Charm, that
hides him until he enters the invisible hallway through the invisible
door. (Which, BTW, explains why the Malfoys, and Bellatrix after she
was freed, didn't just show up at 12 GP after they talked to Kreacher.
They knew that Kreacher belonged to Sirius and may have guessed that
Sirius was hiding in that house, but they didn't know that it was
Order HQ and couldn't have see it even if they guessed.)

So, Lupin is landing on an invisible step, but he's not invisible
himself until he enters the house. So how does he avoid being seen
without an Invisibility Cloak for the few seconds it takes to land,
regain his balance, and open the door? If Apparating very precisely
onto the front step keeps Lupin from being seen (204), why should it
matter if Harry's elbow sticks out of the Invisibility Cloak for a
second if he's on the top step when it happens? (224).

Carol, who thinks she's found yet another inconsistency in the seventh
book