Copeland begins with a tenacious retiree named Alice looking for the truth about her orphaned father’s family. Using her story, Copeland walks the reader through how genetic testing works, with just enough detail to leave you confident in the results (seriously, this is how schools ought to teach biology). But even if 20 pages later you’ve forgotten the difference between autosomal and mitochondrial testing, you will be able to follow along without any trouble. The gist of it is, while some genetic claims are tricky (ancestral heritage is constantly being redefined), others like relative matches are remarkably accurate.

If you are concerned about keeping your genealogical privacy, that ship has largely sailed. A few decades ago, finding that needle of a relative in a haystack was unlikely. But as more people post their DNA online, genetic genealogists can go backward in history to find a common ancestor and then, with public records and detective work, discover a relative in the present day. That’s how they caught the Golden State Killer.

Like any good reporter, Copeland casts her net wide when looking for sources to interview. She talks to people whose casual test revealed an NPE, or “Non Paternity Event” (your dad is not your dad!). One company, AncestryDNA, even has a highly trained customer service team of empathetic listeners to help people dealing with unexpected results. Copeland seeks out adoptees searching for their biological parents, and the offspring of sperm donors who discover they have dozens of siblings. She looks backward at the ominous history of eugenics, which was harnessed by the Nazis and by racist authors today. She examines the efforts to help African Americans trace their heritage, since they don’t show up on census records before 1870. She even reports on people who post on the white-supremacist website Stormfront who discover they are not as white as they thought.

Then there is the financial angle. After reading about the impressive profitability of genealogy companies and their growth potential, you may want to call your broker. As one early entrepreneur states, “This is a multibillion-dollar industry and nobody’s noticed it yet.” Certainly there are a lot of companies doing DNA testing, 246 in 2016 alone, with AncestryDNA dominating with the biggest database. It may remind you of the early days of the Internet, except in this instance, the customers are also the product.

But it isn’t just finding relatives. Companies like 23andMe specialize in identifying genes like BRCA1 AND BRCA2, which are linked to breast and ovarian cancers, and genetic variants for diseases like cystic fibrosis and Parkinson’s. They are partnering with research institutions like Stanford and the National Institutes of Health and pharmaceutical companies like Pfizer to do studies that are just beginning to bear fruit, with the promise that one day scientists can pinpoint with precision the genes that cause a disease. There is a case to be made that companies ought to be paying for you to spit in a tube, not the other way around.

How would we feel if our genetic information was used by companies to deny us health care? Do you even want to know if you carry genetic markers for Alzheimer’s? Is anyone reading the fine print for all these DNA testing companies? Copeland does (so that you don’t have to) and is still pretty mystified.

At times reading this book, you get the sense that we are on the edge of some brave new world. It’s exciting, and a little frightening too. Even if you think (like everyone does) that your family tree holds no uncomfortable surprises, Copeland will make you ponder just how much stock we put into our genetic heritage.