Part two starts off with Robbie Turner navigating two privates through the countryside of World War II France. We discover that Turner has been injured, and has shrapnel in his side. We are unclear of the exact year, but England is on the retreat back towards the North and France has been occupied by Germany completely, so it is safe to assume it is pre-1942.
The three British soldiers, Robbie Turner and Corporals Mace and Nettle, take refuge in the barn of an old French women somewhere near Arras. They are en route to Dunkirk where they can catch a Naval ship back to England. The French woman's two sons return to the farm after a family-seeking mission for victims of the war and share dinner and wine with the British soldiers. When Turner attempts to sleep, his thoughts turn to nightmares of the awful scenes of war and his memories of prison.
We learn that Turner spent three and a half years in a British prison for his crimes against Lola. We also learn that during that time, Cecilia remained supportive of his innocence, abandoning all the members of her family completely. She is now a nurse and living in London. Only six days out of prison, Turner was recruited to the army (the war had yet to begin). He begins training immediately, further delaying the time he gets to see Cecilia. He is able to meet with her once at a café in London, but the rendezvous is dissatisfying. It is fair for the reader to assume that Robbie has made an arrangement to reduce his prison time by serving in the British Army in the war agains the Germans.
The two plan to spend two weeks together before Turner has to report to the Army. But before this can happen, England declares war on Germany and their opportunity is missed. Through the retelling of letters, the reader learns of Turner’s encouragement for Cecilia to reach out to her family, if even to let them know where she is. Despite his efforts, Cecilia refuses to do so, disgusted with the way the accused him of rape and saw that an innocent man be put in prison based on the shaky testimony of a 13 year old girl.
In a final letter from Cecilia to Robbie, it is revealed that Briony has passed on her opportunities at Cambridge to take up nursing as well. Briony is seeking a meeting with Cecilia in which Cecilia interprets to be an attempt to come clean about her false statements on that fateful night. Unsure of what she should do, Cecilia seeks Robbie's opinions through a letter to him.
The change in time and setting represents a change in literary form for McEwan. The first part was written under the heat of an England summer, was Romantic in style (plenty of references to nature, water, vegetation) and now we are entering the second part which will be a war-memoir. The move from a country-home traditional novel style to historical fiction demonstrates Atonement's sweep through the history of English literature. Writing in only one form would not be enough for Briony Tallis, she needs to exercise her brilliance by different means.
Right away we are given a "leg in a tree." This disembodiment of human body parts foreshadows the horrors of war to be described on the next one hundred pages. The leg Robbie spots in the tree takes him back to that night in 1935. Recall that when Briony went to look for the twins, she noticed her mother's leg in the window and, it too, appeared "disembodied." Also, one of the twins is missing a piece of their ear. There is a literary motif at play here, and McEwan is pointing out just how simply parts of oneself can be torn or dismembered.
The only privacy Robbie gets while on his Odyssey back to Dunkirk is through a map, suggesting that there is only direction in his life where no other people are involved. It is the rest of humanity, and not Robbie himself, who have destroyed his path home for him (Briony, Lola, the war). The Frenchman comments on how the war is repeating itself after WWI pointing to the cycles of guilt and forgiveness in humankind.
The narrator introduces the idea of "hope" during Robbie's march. Her atonement is building. In Part One she admits guilt; now she employs hope. On page 192, Briony relates Robbie and Cecilia to so many other famous romantic couples who have overcome great odds for their love. Neither Robbie as character in her story, nor Briony as narrator, are willing to let go of their dependence on literature (notice it was in a library where Briony observes Robbie and Cecilia consummating their love).
This entire section is unlike the rest in that its optimistic. Robbie is determined, like Leon's attitude, that all will turn out for the best. He will make it to Dunkirk alive and back to London. Surprisingly, this happens.