I always enjoy Clements novels. They are well written and researched. This is the latest in the group centred around the start of World War Two in Cambridge where the lead character Tom is an American history professor. This is a spy novel series and since many characters appear in all and make reference to events that happen in other novels it would be helpful to read those first. You won't struggle to identify the villain but the central characters are threatened and I felt I cared enough about them to read the novel quickly and with enthusiasm.