Swamped

Nothing seems obviously disturbed, but you notice a length of string on the floor. You don't remember that being around earlier.

Looking up, you see a throwing knife lodged in the ceiling, with a bit of string tied to the handle. So maybe he was trying to investigate something up there, and you knocked the string down when you tackled him. Or maybe he just pulled too hard on it, tough to say.

You're baffled as to what he could be trying to do with it. Is he looking for something up there? The knife hardly seems like the best tool for the job if that was it, although it's probably the only thing at hand.

Well, there's a single weight lying on the floor here. You think you can reach the knife if you stand on that. You pull it out a bit and step on it, then reach for the knife and pull.

A tile of the ceiling comes out with it. You don't see anything behind it, though - just wood. Doesn't look like there's even a gap for something to hide in.

But then you look a little more closely at the back of the tile in your hand, and you notice something odd about it.