In the fourth and final volume of The Straits Quartet, Charlotte Macleod is the English concubine. Her love affair with Zhen, wealthy Chinese merchant, is an open scandal to both the English and the Chinese communities. Singapore in 1860 is a vice-ridden town filled 'with the dregs of humanity from two continents'. Opium makes up half of the British Empire's trade in the East and, from Singapore, the Chinese triads control the vast distribution of chandu, refined opium, which is spread throughout the south seas. Turf wars are fought on the high seas and on the streets of Chinatown to control the mighty profits of this trade. The colonial government, impoverished and ineffectual, can do nothing about it. Only the Chinese godfather, the lord of the kongsi, has that power through his control of the coolie, prostitute and opium trade. When Zhen is forced to become the godfather of the kongsi, cracks appear in Charlotte's world and when Alexander, her son, unaware of his true paternity, arrives from Scotland and begins a secret and incestuous affair with his own half sister, it explodes. Opium, murder, incest, suicide, passion and love. A heady combination in the sin city of the south seas.