From The Anarchy: The East India Company, Corporate Violence, and the Pillage of an Empire, by William Dalrymple (Bloomsbury, 2019), Kindle pp. 144-145:
That evening [20 June 1756], having ‘swept the town of Calcutta with the broom of plunder’, Siraj ud-Daula was brought in his litter to visit his new possession. He held a durbar in the centre of the Fort where he announced that Calcutta was to be renamed Alinagar, after Imam Ali – appropriately for a prominent city in a Shia-ruled province.
So far, the surrendered garrison had been treated unusually well by Mughal standards: there had been no immediate enslavement, no summary executions, no impaling, no beheading and no torture, all of which would have been, in the Mughal scheme of things, quite routine punishments for rebellious subjects. It was only after Siraj had left that things began to fall apart.
Many in the Company’s garrison were still blind drunk, and in the early evening one intoxicated soldier who was being stripped of his goods became incensed and promptly pulled out a pistol and shot his Mughal plunderer dead. Immediately the tone changed. All the survivors were herded into a tiny punishment cell, eighteen feet long by fourteen feet ten inches wide, with only one small window, little air and less water. The cell was known as the Black Hole. There, according to the Mughal chronicler Yusuf Ali Khan, the officers ‘confined nearly 100 Firangis who fell victim to the claws of fate on that day in a small room. As luck would have it, in the room where the Firangis were kept confined, all of them got suffocated and died.’
The numbers are unclear, and much debated: Holwell, who wrote a highly coloured account of the Black Hole in 1758, and began the mythologising of the event, wrote that one woman and 145 Company men were shoved inside, of whom 123 died. This was clearly an exaggeration. The most painstaking recent survey of the evidence concludes 64 people entered the Black Hole and that 21 survived. Among the young men who did not come out was the nineteen-year-old Stair Dalrymple from North Berwick, who only two years earlier had been complaining of Calcutta’s cost of living and dreaming of becoming Governor.
Whatever the accurate figures, the event generated howls of righteous indignation for several generations among the British in India and 150 years later was still being taught in British schools as demonstrative of the essential barbarity of Indians and illustrative of why British rule was supposedly both necessary and justified. But at the time, the Black Hole was barely remarked upon in contemporary sources, and several detailed accounts, including that of Ghulam Hussain Khan, do not mention it at all. The Company had just lost its most lucrative trading station, and that, rather than the fate of its feckless garrison, was what really worried the Company authorities.