Got a flat as I was headed out of my driveway the other day. I could hear the hiss, and stopped before I had gone more than 100 yards.

Once home, I removed the tube, and found a single pin-prick type puncture, in the middle of the tread. I thoroughly inspected the tire, but could not locate anything sharp, either on the inside or on the outside.

The tube had come with the bike (a craigslist purchase) over 2 years ago, so I don't know how old it is. I have a spare tube, as well as a patch kit. My question is, which should I use?

I ride on roads, and am preparing for a metric century in a couple of weeks.

Thoughts?