The world’s most influential management consulting firm, McKinsey & Co., might just be one big con. So says Duff McDonald in his new book The Firm, which offers a deep dive into the top-secret world of the über-elite organization. While McKinsey is undeniably made up of heavy hitters—it produces more Fortune 500 CEOs than any other company—its track record begs the question, are they worth the hundreds of billions struggling companies pay out annually for their advice? A few of the firm’s most infamous misses: McKinsey advised GM in a failed attempt to compete against Japanese automakers and told AT&T that the cellphone market would include 900,000 subscribers (it was off by 108 million). Oh, and Enron. The New York Times awkwardly notes that the paper itself is not just a critic, it’s also a client.