This was the fifth and final book in the series and I was glad that I had listened to at least one of the earlier books. I felt I needed some background to the The Peacemaker, a vital character who had previously been present only as an alias.
The three main characters are the Reavley brothers, Joseph, an army chaplain and Matthew, an intelligence officer, and their sister, Judith, an ambulance driver. Joseph and Judith are serving at the Western front but Matthew has been away from most of the action. He makes his way to the medical post where his siblings are, because he needs to bring a German, von Schenckendorff through the lines to reveal to the authorities in England, the identity of The Peacemaker.
Unfortunately their plans are thwarted by the ugly murder of a nurse at the medical station, which results in a murder trial and Matthew becoming implicated.
While the murder and its solution is unnecessarily drawn out, it is at least believable, but I found the journey home stretched belief, being too full of lucky coincidences.
I had previously listened to an abridged audio book version of Angels in the Gloom, number 3 in Anne Perry's WWI series. Being abridged, it contained all the pertinent facts without the drawn out explanations I found in the unabridged version of We Shall Not Sleep. In particular, the author really laboured the issue of soldiers returning home after the war - how would they readjust, and who would the women back home marry now their men had fallen?
My personal recommendation would be to listen to this series in abridged form, rather than in full. This will give the flavour of the war without the repetitions and drawn out explanations.