I got it from the library as a kid. I don’t know the title or the author, but the plot involved someone stealing odd items like a stream and maybe a shadow. Or something like that. That’s all I remember. Does this ring a bell with anyone?
Yet another opportunity to tout the “Solved Mysteries” page run by Loganberry Books: http://www.logan.com/loganberry/solved.html .
Darn, booklover beat me to it!