Joining Together - Group Theory and Group Dynamics by Johnson and Johnson 10th Edition.
I borrowed this book and read the first 20 pages. I had a lightbulb moment about staff management. I continued to read on another 80 pages and had several of my beliefs validated. I had to give the book back. I am now waiting on my copy to arrive so I can re-read those pages, and read the next several hundred pages.
Thoroughly recommended it.