What are the motifs in A Test of Wills by Charles Todd?

The idea of persistence runs through many murder mysteries. The sleuth must be methodical, organized, and persistent to break through suspects' natural resistance to intrusion into their personal business. The witnesses tell what they think they know, but it is the persistent investigator who digs for what they really know. Ian Rutledge personifies this type of persuasive, persistent detective. He keeps circling back and circling back. He gets a new piece of information and he circles back to see his witnesses reactions. He persists when things seem bleak, he persists in the face of upper-level pressure to find the quick answer, and he persists against all boundaries of proper, polite behavior. He must, because he is driven to find the answer to the puzzle, and the resolution to the mystery.