Investigate the running water

You get up and get out of bed. You are curious who would be up this time of night. You quietly creep up to the door and see if you can listen in. No luck, all you can hear is water running. You try to peer through the cracks in the door, but you can see nothing.

You remember that the closet in the master bedroom runs behind the bathroom a ways, and if you are going to hear what is going on, you figure you will have a better chance there.

Stumbling over the boxes stacked there, you find the light switch hanging from the ceiling. You turn on the light, and locate a good spot to listen in. Strangely enough, there is a small sliding piece of the wall here. You start to wonder what it is for, but suddenly you remember the mirror on the wall - could it be a 2-way mirror?

Remembering your b-movie scenes, you shut off the light in the closet, and slide the piece of wood aside.