Cycling 15:00  2.3 mi (6:31 / mi)
Took the road bike to work to get in a midday ride. Front tire was firm, rear was a bit squishy, but I didn't bring the pump. Beginning the ride, I went around in the parking lot, trying to get the feel for the squishy rear tire. It felt a bit as if it were moving sideways occasionally, but it wasn't flat, and I didn't see anything out of the ordinary. Brakes were working normally.
A couple of miles in, the sound is worse, but nothing looks wrong. Then thwup I notice the tire is not sitting firmly on the rim. Then I notice there's no tube directly underneath where the tire is offset. Ok, no patch kit will fix a blowout, and I don't have a spare.
I try to ride it gently back, but the tube, instead of having 0 ends, goes quickly from 2 ends to 4 ends and gets twisted around the rear axle. Bleah.
Walking 30:00  2.0 mi (15:00 / mi)
I walked it back to the plant. Saw two cyclists about a mile out, who offered me a spare tube, but I said I could probably get back more quickly by continuing to walk rather than (take one of their spares,) change the tube, and then continue up the hill.
At least it wasn't raining.