IF - Shadows

This is my Illustration Friday entry for this week:

Two Strange Beings | 9x12 | pastel

"One evening, while he was lying there alone... he saw two strange beings creep out of the tall bracken near him."

This illustration is the result of a fun SCBWI Westside Illustrators project. I was assigned the above quote from a children's book without knowing the origin.

Would anyone care to guess what childrens book this came from?