Simon Parkin's extensively researched book on the the Isle of Man's WWII Hutchinson internment camp, The Island of Extraordinary Captives, explores an often overlooked area of wartime history about which I knew a very little. It is truly eye-opening.
In In Other Words, Jhumpa Lahiri examines - briefly but yet in depth - the barriers and boundaries inherent in acquiring another language, and chronicles her long-term immersion in Italian which led her to write this book in that language itself.
Rumer Godden's novel A Fugue in Time overlays past and present in a multi-generational story, the technique she used later to great effect in China Court. These and many other books are discussed in her second volume of autobiography A House with Four Rooms which blends the personal and professional in charmingly anecdotal, discursive style. I loved it.