The good news: this idiom has nothing to do with ghosts
Meaning[]
The moving spirit is the person who came up with an idea. What sense the idiom is taken in depends on how good the idea is.
Use in Normal Speech[]
After a good idea.
"Where's the moving spirit behind Operation Mayfair - he or she is a genius!"
After a bad idea.
"OK, guys, who's the moving spirit behind this non-starter of an idea? I have a bone to pick."