While the investigative process is a staple of all crime fiction and might simply be seen as a plot device, in Death Cloud, it functions as a recurring motif that relates to the theme of Becoming Holmes. When the story begins, Sherlock has no prior experience or conceptual knowledge of how to solve a crime. He is merely driven by curiosity and the desire to help Matty.

However, he quickly demonstrates a dogged determination to get to the facts, even when appearances seem to contradict the conclusions that he reaches. Initially, all the adults in his world discourage him from pursuing the mystery of the death cloud. Despite these injunctions against getting involved, Sherlock takes two steps that set him at odds with the authorities in his life. He collects a sample of the yellow dust surrounding the second victim and later enlists Matty to convey him to a nearby town where he can question an expert on the matter. Both moves prove to be wise in retrospect. The yellow powder is shown to be pollen, and the expert debunks the theory that bubonic plague was responsible for the deaths in Farnham.

Sherlock will go on to investigate the warehouse in town, risking his life in the process.