I snapped, but did not post this picture:
I called a plumber, but the soonest he could get to us was several days later after, coincidentally, the temperatures rose from -30C to a gentle -10C. The plumber showed up, augured the drain and had things working in no time a-tall.
Then the temperature dropped again and - lo and behold - the tub plugged up again. So tonight, Steve got serious and ripped that powder room a new one. Hole, that is. So now we have this:
Since we're in the powder room anyway, I figure I might as well show you some "glam shots," so here you go: