The Deceivers by Nicholas Meyer

5.38

India, 1825: the country lives in mortal fear of cult members known as the “Deceivers." They commit robbery and ritualistic murder. Appalled by their activities, an English military man, Captain William Savage, conceives a hazardous plot to stop them. In disguise, he plans to himself become a “Deceiver” and infiltrate their numbers. Ever present in Savage’s adventures is a sense of dread; he is in constant fear of betrayal and vengeance and also undergoes a disturbing psychological transformation as he experiences the cult’s blood lust firsthand.