Prime Minister Narendra Modi handpicked a trusted bureaucrat, little known outside India's financial circles, to spearhead a radical move to abolish 86 percent of the country's cash overnight and take aim at the huge shadow economy.
Hasmukh Adhia, the bureaucrat, and five others privy to the plan were sworn to utmost secrecy, say sources with knowledge of the matter. They were supported by a young team of researchers working in two rooms at Modi's New Delhi residence, as he plotted his boldest reform since coming to power in 2014.
When announced, the abolition of high-value banknotes of 500 and 1,000 rupees ($7.50 and $15) came as a bolt from the blue.
The secrecy was aimed at outflanking those who might profit from prior knowledge, by pouring cash into gold, property and other assets and hide illicit wealth.
Previously unreported details of Modi's handling of the so-called "demonetization" open a window onto the hands-on role he played in implementing a key policy, and how he was willing to act quickly even when the risks were high.
While some advocates say the scrapping of the banknotes will bring more money into the banking system and raise tax revenues, millions of Indians are furious at having to queue for hours outside banks to exchange or deposit their old money.
Laborers have also been unpaid and produce has rotted in markets as cash stopped changing hands. Not enough replacement notes were printed in preparation for the upheaval, and it could take months for things to return to normal.