Brakes stuck then gone completely

[NRS]

Hi,

I have a MX-5 NB/Mk.2 (1999 model). This morning one of the calipers seemed to have got stuck - so much so the wheel was dragged without rotating over snow/ice when I reversed in my parking place this morning. I wondered if it had frozen, and when I drove a little further on the drive it popped and started rolling. However when then applying the brakes they basically have stopped working. There is no leaking fluid where the car is, and the brake fluid levels are fine. I'm guessing the brake master cylinder has probably failed? Anything else it might be?

Thanks!