They were probably referring to the Siege of Cawnpore (Kanpur) during the Indian Rebellion of 1857. Following the mutiny of the East India Company soldiers which formed the garrison, Major General Hugh Wheeler and roughly 900 other Brits and loyal sepoys, most of whom were not soldiers, fortified themselves outside the city. After about 20 days under siege, Wheeler made an agreement with Nana Sahib, the commander of the rebel forces. The British were to be provided boats to take them along the river to Allahabad. However, as the British left the encampment and reached the river, they were attacked by the rebels and most of them were killed. About 120 women and children were taken prisoner. Since very few of the defenders actually survived, it's not entirely sure what sparked the massacre, and claims have alternately been made that it was provoked by the British, planned by the rebels or simply a confusion of orders.
In any case, the captured women and children were taken to Bibighar in Cawnpore, where they were held until the 15th of July. Hearing news of approaching British forces, the order was given to execute the captives, which was done by a combination of shooting and execution with meat cleavers. When the British arrived they were disgusted by what had gone on and forced rebel captives to lick the courtyard clean. Other choice punishments included forcing their Hindu and Muslim captives to eat pork and beef. While not the only atrocity committed against British civilians by Indian Rebels, the Bibighar massacre was used as a major example of both Indian duplicity and barbarity during the campaign.
For further reading I'd suggest the following series of articles:
Rudrangshu Mukherjee, "'Satan Let Loose upon Earth': The Kanpur Massacres in India in the Revolt of 1857". Past & Present, No. 128 (August 1990).
Barbara English, "The Kanpur Massacres in India in the Revolt of 1857". Past and Present No. 142 (Feb 1994)
Rudrangshu Mukherjee, "The Kanpur Massacres in India in the Revolt of 1857:Reply". Past and Present No. 142 (Feb 1994)