Getting into math ten years after a BA in English I got a BA in English at a pretty good school, spent the next 10 years in a fruitless pursuit of screenwriting with a day job in a legal department, and now that I'm sick of all that, I'd like to do something mathy. And it seems pretty clear that that's going to require going back to school.

Since this is a HUGE redirection -- a ridiculous one, really -- I assume I should get a second BA/BS before even considering a masters, right? I did well in math in school, but I left off at single variable calc. (I'm currently studying linear algebra on my own and loving it.) But what, really, are my chances for even getting into a decent second bachelor's program?? I'm thinking of taking college extension classes to get more experience and recommendation letters for that purpose. If I get some online bachelors degree (EDIT: or a post-bac), are any (reputable) masters programs even going to consider me?? 

You may well ask what my eventual goal is, but I'm at such a basic level that I'm not sure that that question is all that relevant. If I were to pick a goal just for the sake of aiming for something, getting a job in statistics sounds interesting, but who knows what I'd want to do after getting a second bachelors. I'd like to try my hand at research, but that sounds way too pie-in-the-sky given my background.

Thanks for any advice or feedback.
If you want to go into math, should you get a BSc?

I'd say "yes". It often is quite doable to pick up a new subject on your own if you have academic experience, but English and Mathematics are so far apart that I'd doubt there would be a lot of synergy. Mathematics has its own way of thinking, which is probably picked up best by going through an undergrad degree.

Should you go into math?

Enrolling for a degree is of course a rather strong decision. In my experience quite a few of those who start anew later in their lifes drop out rather early. Maybe taking an online course first could both be a good preparation if you go through with it, and helpful to figure out if you really want to it.

Can you get in somewhere?

I don't know about your country, but both the UK and Germany often have places reserved for mature students, which have fewer formal requirements. So in those countries, getting into a decent program would be quite doable.

A final comment

For me at least mathematics is great fun. If you believe you'd like it, and you are willing to put in the effort, give it a try.