A country gentleman, Sir Stafford Cripps - ascetic, vegetarian, and a devout Christian with a lucrative career at the bar - cut an incongruous figure in British politics of the 1930s. By the time war broke out, his position among Labour's most radical backbenchers had made him an outcast. It was his fortuitous appointment as ambassador to Moscow in 1940 which secured for him a prominent position in the War Cabinet and later on a key role in Attlee's Labour government. His diary, which he meticulously kept while in Moscow, describes the metamorphosis in his political fortune. As significant is...