Early on in the 1940 novel “Twilight in Delhi,” men in a Shahjahanabad market discuss how much money they’re making thanks to the 1911 Durbar, and how much more they’ll make when Delhi becomes the new capital.

Anyone who has read about the Durbar will recognize how anachronistic that conversation is. It might not seem possible to keep something as major as plans to change your capital and build a brand new city secret, but right up until the afternoon of Dec. 12, 1911, only a handful of people consisting of the king and queen, Viceroy Charles Hardinge and his executive council, the Secretary of State for India and a few others knew anything about it.

Those who did know about it referred to the plan by the codename “Sesame.” The queen wasn’t told about it till the party arrived in India, according to architectural historian Robert Grant Irving. The viceroys of the provinces concerned weren’t told a thing till the night of Dec. 11....