Created in the aftermath of World War II, the Central Intelligence Agency relied on women even as it attempted to channel their talents and keep them down. Women sent cables, made dead drops, and maintained the agency's secrets. Despite discrimination – even because of it – women who started as clerks, secretaries, or unpaid spouses become some of the CIA's shrewdest operatives.

They were unlikely spies – and that's exactly what made them perfect for the role. Because women were seen as unimportant, pioneering female intelligence officers moved unnoticed around Bonn, Geneva, and Moscow, stealing secrets from under the noses of their KGB adversaries. Back at headquarters, women built the CIA's critical archives – first by hand, then by computer. And they noticed things that the men at the top didn't see. As the CIA faced an identity crisis after the Cold War, it was a close-knit network of female analysts who spotted the rising threat of al-Qaeda – though their warnings were repeatedly brushed aside.

After the 9/11 attacks, more women joined the agency as a new job, targeter, came to prominence. They showed that data analysis would be crucial to the post-9/11 national security landscape – an effort that culminated spectacularly in the CIA's successful effort to track down bin Laden in his Pakistani compound.

Propelled by the same meticulous reporting and vivid storytelling that infused Code Girls, The Sisterhood offers a riveting new perspective on history, revealing how women at the CIA ushered in the modern intelligence age, and how their silencing made the world more dangerous.