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Referenced when discussing French politics being split, with the phrase 'as anyone who's read The Dark Valley will know' - indicating it's a book about 1930s European politics

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Explicitly mentioned as 'a famous book by John Lukacs, the historian' about the critical days in late May 1940 when Britain decided whether to fight on or negotiate with Hitler. James describes it as 'completely brilliant' on the cabinet meetings during this period

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Mentioned in passing when discussing assassinations - 'Hilary Mantel wrote a book about her short story about the assassination of Margaret Thatcher' - referring to her short story collection