Where did Tristan go?

I had my first scare. Tristan and I came home from some appointments we had in the afternoon. He has been doing well on the stairs so it is not uncommon for me to walk in the door with him, close the door, and walk either upstairs or down. In this case I went to the basement. I went to the computer and noticed that Tristan did not follow me. This is not that uncommon as he will sometimes play with the light switch. A couple minutes went by and I noticed that he still was not down here so I went to get him. When I got upstairs he was not there... I paused...no Tristan. Then I heard a faint cry and my heart sank. I walked down to the landing where the door is and still no Tristan. I listened... again, I heard a faint cry. I then opened the front door and there he was standing at the front door crying. I could not believe it. He masted the front door. Thank God this was all over the span of about 5 minutes but it seemed like forever!