A Pattern of Shadows is set in August 1914 and looks at the shattering effect the approaching conflict has on the lives of three young people who have grown up together in the same Kentish village. Alice Campion keeps house at Rendle Manor for her father, Sir Douglas, and younger brother, Ben. She is in love with Peter Crawford, a professional soldier and eldest son of one Sir Douglas's tenants. However, she becomes aware of a mystery over Peter's birth which could affect their future together. Ben sails to America as war is declared on a pre-arranged visit. Meanwhile Peter embarks with his unit for France.
Sir Douglas decides to turn Rendle Manor into a hospital and sends Alice to London to a meeting at the Local Government Board, where she makes an astonishing discovery about herself. She returns home confused and unable to concentrate.
In France, Peter is involved in the general retreat from Mons and is wounded. Ben, emboldened by his experiences, returns from America to join the Royal Flying Corps, and with the news he is to be married. Peter's mother, Edna, finally divulges the secret that will allow Alice to marry Peter. However, no one has heard from him for over a week. The novel ends at the beginning of September with Alice hoping for a letter, but determined not to lose heart. The epilogue, which looks back at events in the war, is set in 1930.