The Four Men of the title are British WWI veterans who decide to work secretly against enemies of the country. They aren't above a bit of murder or sabotage to serve their ends, but they consider themselves to be true patriots.

Eccentric Cambridge archaeologist Horatio Smith takes a group of British and American archaeology students to pre-war Nazi Germany to help in his excavations. His research is supported by the Nazis, since he professes to be looking for evidence of the Aryan origins of German civilisation. However, he has a secret agenda: to free inmates of the concentration camps.

A group of travellers, each with a personal problem that they want to hide, arrive at a mysterious Welsh country inn. There is a certain strangeness in the air as they are greeted by the innkeeper and his daughter. Why are all the newspapers a year old? And why doesn't Gwyneth seem to cast a shadow?