Cybersecurity Expert Eric O’Neill achieved his first bestseller on Amazon with his new book Gray Day. After just one week of release, the true-life spy story sits squarely in the top 10 for Intelligence and Espionage books. In Gray Day, O’Neill recounts how, as a young F.B.I. agent, he was recruited to take down the most notorious spy in U.S. history—Robert Hanssen.

The story of O’Neill and Hanssen has previously been made into the movie Breach, starring Ryan Phillipe as Eric O’Neill and Chris Cooper as Robert Hanssen, and retold in several books, but this book is the first to provide O’Neill’s insider look at the takedown.

O’Neill shows what it’s like to attempt to maintain a normal life—going to law school and maintaining a marriage—all while pretending not to be on a secret assignment. However, stress takes its toll on both his education and marriage as he tries to fool Hanssen into making a mistake. A great read for anyone interested in intelligence, espionage, and cybersecurity.

Kyle Crocco is the Content Marketing Coordinator at BigSpeak Speakers Bureau, a graduate of UC Santa Barbara, and the lead singer of Duh Professors. He regularly publishes business book reviews and thought articles on Medium, Business 2 Community, and Born 2 Invest.