I somehow misplaced the envelope and didn't realize it until I was in her incall. I had enough money stashed in the car and quickly went back to my car to get the money and proceded with the wonderful session.
Though I didn't relish the thought of losing the money, what I was really fearful of was that I left the envelope, with the money, somewhere my wife would find it. I couldn't come up with a good explaination for a stash of cash in an envelope.
I looked for the envelope in the car one more time and found it behind a seat.