About a dead mouse in the wall…and the resulting stink. I called an exterminator, who said he could not even try to find the corpse, and suggested just waiting out the smell, which is already abating.
There are not many tricks that will succeed. I had the same thing happen two years ago, and I broke into the wall in several areas with no success. An exterminator searched the wall with his TV scope, a little like a colonoscope, also without success, so he charged only $50.00. A little later, a fly discovered the corpse, laid hundreds of eggs, which hatched into maggots that escaped to my porch and caused my wife to go absolutely ape and destroyed all she could find. Then came hundreds of flies, which I dispatched with a spray; the next few days fewer flies showed up, and on the third day, fewer until all were gone. By that time the smell began to fade, all was sweet again. Incidentally, using odor killers such as Febreze will not work as long as the source of the stink is still there. If you have mice and know where they are, using plastic traps are the best way to get ‘em all, plus closing every possible access hole in the house, the foundation and the wood sill on top of the foundation. To locate these holes, go in the basement on a bright sunny day and turn out all the lights and light sources; you may see holds that you would otherwise miss.