Because of what it looked like when the man went through it, Seeing the questioning look on Dan's face, he went on "If door swung out, we'd have seen it. If it swung in, we would've seen the opening in the wall as he went through it.
"But we'd have seen a big opening if the door slide up, too," protested Nate.
The boys examined the area around the hidden door carefully. Dan bumped Ron, and he dropped his flashlight. Ron put one hand on the wall as he leaned down to get it.
Dan let out a cry, "Ron, you did it! The door sliding to one side."
Ron straightened up, amazed. The door had slide to the right, leaving a crack one-foot wide. It was just enough space for the man to have slipped through.