My picture book synopses (more like pitches) usually follow this route (using Little Red Ridinghood):
When Little Red tells a wolf she's going to Grandma's house, the wolf gets there first and gobbles Grandma up. Will Little Red be his next victim? Not if the Woodsman has anything to say about it!
Silly, I know, but I hope it gives you a framework. Good luck!
Jody