If you haven't read Regeneration, you are making a big mistake if you read The Eye in the Door before Regeneration. Regeneration sets the stage for The Eye in the Door and provides much background information that you need to appreciate this book.
Those who liked the first book in the Regeneration trilogy, Regeneration, will absolutely adore The Eye in the Door. The characters from Regeneration return, and you have a chance to find out the consequences of the treatments they received from Dr. William Rivers in Regeneration. Pat Barker builds on the tensions, damage, doubts, and despair of mid-World War I to show how much more desperate matters were for the British by the spring of 1918.
In developing these themes, Pat Barker does a masterful job of explaining how a soldier has to operate both by emotion and by objective distance in order to function. From there, she helps us use the crucible of war to see how that duality is important to everyday functioning for all people.
As the title indicates, the book builds on a central metaphor of everyone being under observation as doubts build about Britain's ability to win the war. Those on the margins are most under pressure and at greatest risk.
I thought that the portrayal of Lieutenant Billy Prior was brilliant. He comes across as the kind of complex, interesting character that can help us learn a lot about Ms. Barker's messages for us. The eye metaphor is nicely developed in the context of Billy's life.
Brava, Ms. Barker!