Cat pee smell in carpet, but no actual cat pee - what have I done???

This is weird (and requires some explanation) so bear with me. The other night Mrs. rainy and I were sitting in the living room when we detected the undeniable odor of cat urine. Odd, since we don’t have any indoor cats. Thorough investigation yielded nothing - no chew toy the dogs take in and out smelling, no odor around the outside windows, nothing. We give up the hunt and go to bed. It is still there the next day and getting stronger.

My guess is that I walked through some cat urine in the yard (we have outside cats) and inadvertently tracked in inside on my shoes. So I am down on my hands and knees smelling the carpet. Turns out the area where we accidentally spilled a solution of Epsom salt water was the culprit. It smells exactly like cat urine. I get out the steam cleaner, mix baking soda and water and clean the area – immediately the smell begins to go away. Now, the next morning, as the carpet is drying in that area the smell is returning.

What chemical monster have I unleashed?
And more importantly, how do I get rid of it?!?

Help,

-rainy

Here are 2 links on the chemistry of cat pee:

http://odors.quora.com/Why-Does-Cat-Pee-Smell-So-Bad

Apparently as cat pee is broken down by bacteria, it can create new and more smelly chemicals with exotic names. Some industries emit a few of these chemicals, making their neighbors unhappy.

Yikes.

As to how to get rid of cat pee, apparently it can get so bad that removing the carpet or even sanding down the wood floor become the preferred solutions, according to Cheryl Mendelson. That said, a commercial enzyme cleaner or a visit to a pet store would probably be your next step.