Rendezvous at Carchemish

How did Charlotte "Carlo" Fisher, Agatha Christie's governess come to be so far away from Styles in Sunningdale, Berkshire where she lived and educated dear Rosalind, Agatha Christie's daughter?
Wearing the war tunic of the Soviet Union, as an observer for the British Army, Carlo sits in the bombed-out Adlon Hotel reflecting on where her adventure began...on Route 66 with her lover, John Steinbeck. Realizing she is his muse, she knows that he has greatness in him, but to bring it out, she must break his heart.
From this decision, her journey truly takes off as she returns to Britain and the apparent normalcy of the English countryside. Along the way, she meets many varied and fascinating characters from F. Scott Fitzgerald, to Hemmingway, to Tallulah Bankhead.
However, Mrs. Christie may be manipulating circumstances in ways unimagined as Charlotte races to stop a defeated Germany from helping Japan build a nuclear bomb. Two nuclear bombs have already been detonated...was there a third? If so, what does it mean?