New(?) questions about the Unbreakable Vow

[houyhnhnm102]

No: HPFGUIDX 141871

SSSusan again:

> Um.  What we see here is that Snape at *first* agrees with Bella -- 
> that if Voldy has commanded Narcissa not to speak of the plan, she 
> should not do so.  SO IT COULD HAVE ENDED RIGHT THERE.  He could have 
> LEFT it at that.
> 
[...]
> Why did Snape do this?? 

houyhnhnm:

This switch is what convinced me that Snape did not know about the
plan (or maybe he knew that Voldemort was up to something, but he'd
not been able to discover what)
-----------------------------------------------
"The Dark Lord has forbidden me to speak of it," [...]

"If he has forbidden it, you ought not to speak," said Snape at 
once.  "The Dark Lord's word is law."
-----------------------------------------------
In between Narcissa's statement and Snape's response, Bellatrix
interjects:  "Then you ought to hold your tongue," snarled Bellatrix.
"Particularly in present company!"

I don't see Snape as having any kind of plan in this scene.  He's just
dealing with one threat at a time and looking for opportunities. 
First, it is the presence of Wormtail he must turn to good account. 
It's got to look suspicious that the wizard who brought LV back to
life is living in Snape's house and listening at keyholes.  So he
solves that threat by brow-beating Wormtail into the role of a servant.

Then before he can begin to find out why Narcissa is there, Bellatrix,
in effect, accuses him of being a traitor.  He throws the accusation
back at both of them to put them on the defensive (the better to be
manipulated).  All the time he's thinking that here's the closest he
gotten to information that may be of dire consequence.  How can he
work it?

-----------------------------------------------
But Snape had gotten to his feet and strode to the small window, ....
He turned around to face Narcissa, frowning.

"It so happens that I know of the plan," he said in a low voice.  "I 
am one of the few the Dark Lord has told.  Nevertheless, had I not 
been in on the secret, Narcissa, you would have been guilty of great 
treachery to the Dark Lord."
-----------------------------------------------
He goes to the window to compose face and mind for the lie, and
repeats his counter-accusation for good measure to keep both women on
the defensive and therefore unable to observe/question his behavior
too closely.

In "Spinner's End", we get to see Spy!Snape in action for the first
time. He's good. He can think fast on his feet, turn on a dime.  He
was probably congratulating himself on his own cleverness at the very
moment when Narcissa broached the Vow.