"Arguable." She's holding a little black leather-bound book, which is glowing and vibrating violently. "I have higher priorities. Give me my locket and you can have Dumbledore's stupid firebird back. Teach me the Fidelius and you can have your idiot godson too. You have forty-five seconds." 

What. What. You WHAT--

"First of all, die in several fires. Second of all, forty-five seconds to decide or to teach you a proprietary spell most people need six months of practice for. Third of all, fuck you and the walking corpse you rode in on. Fourth of all--"  

"First thing, Sirius please, didn't Harry tell you I'm still alive in here?" 

Wow, what the fuck, Tom hasn't let her actually talk for real since she was seven and a half. She's been trying every ten to fifteen seconds the entire time anyway, of course, because of who she fundamentally is as a person, and wasn't planning to stop even if it never worked for the next fifty years, but she did not actually expect it to. 

This fact is... not helping her blind terror even a little, actually. She does not want to find out what happens to you in the afterlife that Harry seems so sure exists if you die with your soul still stapled to the greatest evil of the generation. 

Sirius now has several additional questions they don't have time for. 

Alright, snap judgment: would Voldemort try this strategy if it was a lie? He certainly could, he is a famously good liar, but the question is whether he would. Pretending to be a terrified thirteen-year-old girl and saying please to someone who knows exactly who he is seems rather like it might strain his pride beyond reasonable limits, given, you know, his entire everything. 

"Fawkes first, locket second, then you oathswear--" this word is not typically used in wizarding English to mean anything less than a real magical Unbreakable Vow-- "that you haven't lied to me and won't renege and then if that goes through I'll teach you the spell." 

(The locket's not a Horcrux and hasn't been since about a week after they found out about Hermione; Harry was only holding off on it because he thought Voldemort didn't know they were after him yet. He is not actually sure if Voldemione knows this but he's sure not going to bring it up. 

"Agreed." 

Then he'll go fetch it. (It's exactly as secure as it was before; why not, when they'd already built the wards? Best case scenario she spends down a bunch of resources stealing it and gets approximately nothing for the effort.) 

While he's downstairs he sends Patronus messages to Remus and to Harry. 

When he returns she's still standing there in the exact same spot, teeth gritted, muttering something arcane that's probably holding the book together. It's turning unsettling shades of mottled glittering orange-green. 

The glowing white dog that is supposed to be delivering a message to Harry is walking in circles around her, sniffing at the book. 

Hate that, thanks. He dismisses it, frowning balefully. 

"What'd you do to them?" he asks, because there's a chance she'll say something that contains nonzero information even if it is a lie. 

"Harry tried to talk down my basilisk, because he is very stupid. Obnoxious firebird in five and it's not my fault if she lights you on fire." 

"It is incredibly your fault if she lights me on fire, you horrid cockroach." 

Harry did tell him about the basilisk but Sirius assumed, apparently incorrectly, that Harry was not planning to try to solo that on a random Tuesday in March. What the fuck, Harry. Sirius can't even be that mad at him because he too has absolutely made adventuring decisions at least this stupid but still. 

Yeah, yeah. How dare he defile the natural order or whatever.

Bargaining chip number one: no longer trapped in a book. 

KRRRRRRRRRRRRAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWWWWK 

... 

...

Wow that sure is a tense standoff involving only two people who are both Unworthy(TM). Fawkes has no interest in this occurrence! Good-bye. 

Shields firebreak shiel.....  no? ... Okay.  

"Locket." 

Toss. 

Nailed it. Perfectly constructed soul-storage mechanism, currently empty of soul because the Gryffindors have done her work for her. She loves being the smartest and cleverest 

(no you're not) 

(shut up, granger) 

ahem, the smartest and cleverest wizard of several generations, thank you very much. 

"Lovely," she says, stringing it around her neck and tucking it under her shirt, next to the comically incongruous gold-and-scarlet tie. "Who's your Vowkeeper, then?" 

(Sirius can see a dozen spells go by under her fingertips as she puts away the book, too, no longer rattling; clearly she needed the locket somehow to stabilize it.) 

This is the Fucking Worst. 

"What happens if I say 'Dumbledore'," he wonders. 

"I laugh at you and leave and you never get your idiot back." 

Fuck, she actually wanted the empty locket more than the spell. This is a stupid game and he is bad at it. 

"Fair enough. Remus Lupin will be here any second anyway." 

Speak of the werewolf. 

"Huh. Nothing's on fire," he observes. "Honestly I'm impressed with both of you." 

He should be, this is so hard. 

Sirius, grumbling, explains the situation thus far while Voldemort smirks at him over his coffee table and waits patiently, his (her?) (their??) time-sensitive goal apparently achieved. It's probably a good thing he doesn't have to deal with this all the time like Harry does, he would actually explode. 

"... look I get it but you really shouldn't." 

Of course he shouldn't. Are you going to stop him, little werewolf? 

He doesn't want to but he's not sure he can face Dumbledore and say he stood there and let Sirius betray them. Again. Fool me once, etcetera. 

"...I could probably fix the trapped in a book thing," he says instead.