There was a wet spot on the carpet in the office this morning, but no signs of a leak in the ceiling. As the wet spot spread, we finally pulled up the carpet to find a combination of plaster, spackling, and 1/4 in masonite on the slab. I started pulling up the wet masonite and chipping up the moist spackling and discovered a 2 inch piece of pine that had been cut into a circle to cover a drain in the floor. We were speculating a sewer line froze and water backed up through the old drain, but then we noticed that while the top of the pine was soaking wet, the underside of the pine was dry, which suggested that the water did not come up through the old drain. I continued to chip back the plaster and spackling until I found dry edges all around the wet spot. The source of the water remains a mystery among puzzling evidence, but we’ll see if we have standing water on the chipped up floor in the morning.