Justin's investigation was in pursuit of the truth behind his wife's death, a truth that is closely guarded by the people in power, people who control the situation. Justin's started the investigation under a guise while he traveled to different countries to uncover the mystery. His investigation led him to both surprising and startling discoveries. Though he was Tessa's husband, he detached himself from her causes. Though Tessa was born rich and beautiful, which makes the reader fall in love with her easily just like the other characters did, she had a strong conscience and was genuinely passionate about helping Africa and its people. Justin's investigation led him to discover things about Tessa that surprised him. It was an opportunity for him to understand her passions and her causes. He also found out startling things about what Tessa and Bluhm were working on and what they had discovered. Justin found out that his wife and Bluhm discovered that a huge pharmaceutical company is manufacturing a drug for tuberculosis which is being tested among Africans. The startling part doesn't stop there; the drug is killing the Africans who were being treated as laboratory rats by the huge pharmaceutical company. This scandal is also central to the story and demonstrates how huge companies can act greedily just because of profit. This is also an issue that illustrates the violation of human rights. Adding more drama and thickening the plot, readers find out that the pharmaceutical company manufacturing the tuberculosis drug has connections with the British High Commission and the British government. This reveals the grim reality of corruption in the government and the corrupt and illegal deals between huge companies and the government. This also illustrates how loud money talks, how greedy and corrupt people are that they can bend the rules and ignore grave injustices for the sake of money. Entwined with these themes are the abuse of power and the use of power to manipulate the minds of the public in order to mask the corruption and injustices going on. This is more powerfully illustrated through...

In order to stop Tessa and Arnold from revealing their startling discovery, power was abused to commit a violent crime and truths were twisted to cover up the crime.
Throughout the story, the reality of inequality was flawlessly described by Le Carre. The difference between how the Westerners and the Africans live and how they are treated was described in an eye-opening way. The prejudice of the Westerners to Africans was also portrayed through the characters by the likes of Woodrow in a way that makes on shameful for it. Another important theme that this book has showed is the way people turn a blind eye to the reality of poverty and injustice. People may feel sympathetic but they don't care enough as Tessa Quayle did to champion the causes they believe it.

Though Le Carre's the Constant Gardener is a work of fiction and though Le Carre implicitly cleared that the book was not based on any true event, the story perhaps may be reflective of reality and thus is credible as testing of drugs on human subjects is being done today and according to Jeanne Lenzer, testing of drugs in overseas has been increasing (qtd. In Brewer). Marcia Angell cited in her article the 1996 clinical testing of the Trovan drug by Pfizer in Nigeria which resulted in deaths and serious injuries of the children involved in the experiment. This is a case similar to the Constant Gardener which makes it credible to an extent.