Angels in the Gloom — Anne Perry

Anne Perry's intense saga of love, hate, obsession, and murder set during World War I follows the travails of an honorable English family--brothers Joseph and Matthew Reavley and their sisters, Judith and Hannah.

In March 1916, Joseph, a chaplain at the front, and Judith, an ambulance driver, are battling not only the Germans but the bitter cold and appalling casualties at Ypres. Scarcely less at risk, Matthew, an officer in England's Secret Intelligence Service, fights the war covertly from London. Only Hannah, living with her children in the family home in tranquil Cambridgeshire, seems safe. But appearances can be deceiving.

When the savagely brutalized body of a weapons scientist is discovered in a village byway, the fear that haunts the battlefields settles over Cambridgeshire--along with the shadow of the obsessed ideologue who murdered the Reavleys' parents on the eve of the war. Once again, this icy, anonymous powerbroker, the Peacemaker, is plotting to kill.