Tony/Natasha ?? i think

I'm looking for a fic where Iron Man is not seen as a good guy.
I think the Black Widow never worked for SHIELD, she's sent to kill Tony, but he and JARVIS already know and he convinces her to work for him.
They end up saving the day at the Battle of New York.
I think the title had something to do with 'burn the world to ash' - something like that.

Natasha/Tony

I recently read: Having Everything yet Nothing and now I'm craving Natasha and Tony stories. They can be romantic partners or just friends. I really want stories that focus on their relationship whatever it may be.

Thanks!