This book's main theme is the disruption and trauma of the refugee experience during the Japanese invasion and occupation of China. Keith Schoppa addresses this from the standpoint of the individual, the community, and the government. In doing so, he reveals how Chinese in Zhejiang, a province he knows intimately, were constantly in danger of being uprooted throughout the course of the war. In tracing the physical and emotional impact of this disruption, Schoppa also touches on such issues as collaboration and the impact of war on regional economic development, and provocatively asks whether one of the most important effects of the war was not the rise of nationalism, as is often argued, but instead a reinforcement of localism.

In a Sea of Bitterness is roughly divided into two halves. The first focuses on individuals, families, and communities. Flight from the Japanese was a traumatic event that uprooted people from their homes, throwing them into an uncertain life on the open road. In addition to the ever-present threat of Japanese attack, refugees were often viewed as outsiders by the communities they passed through. Shelter and transport were hard to find and always expensive, and refugees were in danger of being cheated. Their sheer numbers overwhelmed government attempts at management, and although charities and native place societies were sometimes able to help, for the most part people were on their own. However, amidst the chaos, there were acts of kindness, unexpected reunions with family and friends, and periods of calm reflection. Schoppa eloquently captures these emotions in the account of the famous cartoonist Feng Zikai's flight. Feng set off on a boat along the Grand Canal with his family to find safety. Since it was dangerous to travel during the day, they stopped outside a convent, where a woman kindly cooked them a meal. This brief spell of calm was shattered, not by Japanese bombs, but by four sinister men in black and some Chinese soldiers. They made him nervous, and this led him to mistake the sound of a steamboat for an enemy plane (pp. 68–69). Similar stories, spanning the full length of the war, appear throughout the book. This conveys how over the course of eight years, so many people across the province were forced from their homes, sometimes on multiple occasions. Schoppa relies for the most part on diary accounts and memoirs, which creates empathy between reader and subject. At times, long sections are translated, and indeed the whole of chapter 4 is rendered in this form. This may seem unnecessary to some readers, but detailed comments guide us through the benefits and limitations of using such sources, and warn us when conclusions are somewhat speculative.

It is in the second half of the book that Schoppa's detailed knowledge of Zhejiang comes to the fore. He traces how becoming refugees affected the institutions of government, education, and commerce, and the impact of their arrival on the communities they descended upon. The provincial government in exile fled the Japanese twice, and after 1942, its operations were scattered across towns and villages in some of Zhejiang's most inaccessible counties. Ministries often temporarily suspended operations, while communications were difficult and luxuries such as electricity were rare. Educational institutions were faced with similar problems, although students and teachers managed to continue lessons even when forced to flee several times a year throughout the course of the war. As with government, Schoppa is right to question how far prewar ideas continued to motivate students, although, as he notes, perhaps it was the refugee experience itself that was just as important in giving people a common identity as ideas of citizenship embodied in Republican-era textbooks. Despite also being forced to move, businesses did not always suffer. Some factory owners certainly lost everything to the Japanese, but others relocated safely, and this altered the economic geography of Zhejiang. Raw materials were often in short supply, and patterns of trade relied on smuggling networks, but they brought prosperity to Ningbo and Wenzhou, not to mention smaller towns and villages, which benefited from being outside the Japanese-occupied area.

The chapters on the Chinese scorched earth policy and the spread of plague as a result of Japanese experiments with biological warfare sit slightly uncomfortably within the narrative on refugees. Despite this, both make important points about the devastating impact of military activity on the population of Zhejiang. In a Sea of Bitterness captures wonderfully the impact of the Japanese invasion and occupation on one province in China. It vividly describes the emotional trauma of the refugee experience, and in doing so touches on many aspects of the history of the war in China that will be discussed by scholars for years to come.