Calcutta, 1919. Captain Sam Wyndham, former Scotland Yard detective, has been recruited to head up a new post in the police force. The body of a senior official has been found in a filthy sewer, and a note left in his mouth warns the British to quit India, or else. Wyndham is teamed with arrogant Inspector Digby and Sergeant Banerjee, one of the few Indians to be recruited into the new CID. The case takes them from the opulent mansions of wealthy British traders to the seedy opium dens of the city-- and puts them under pressure to solve the case before it erupts into increased violence on the streets.

"Calcutta, 1919. In the days of the Raj, a newly arrived Scotland Yard detective is confronted with the murder of a British official--in his mouth a note warning the British to leave India, or else"--