What is the main conflict in A Test of Wills by Charles Todd?

In the summer of 1919, Inspector Ian Rutledge of Scotland Yard is desperate to get his old life back after four years of service in the trenches of World War I. When he is assigned to a case in a small English village, he jumps at the chance to see if he still has what it takes to solve a murder, but this case has complications that could end his career and send him back to an asylum a broken man.