Bob wrote:

Follow the BOOM. I would suspect a backstabbed contact on an upstream
outlet burned its way open after intermittent contact arcing.

Ok. I think that'll be the last thing I do before calling an
electrician. It wasn't a loud boom really, was it was definitely
audible. And yes, there is a GFI, in the bathroom, which is live.

I didn't think of the outlets being daisy chained, but yeah, if only
I knew which way the wire goes, I would know which is the last
working outlet...