A young French journalist's riveting and unprecedented look at how today's most ruthless terrorists use social media and technology to reach disaffected youth--witnessed through the undercover investigation that led to her deep involvement with a key member of ISIS.

On Facebook, "Melodie"--a twenty-year-old-convert to Islam living with her mother and sister in Toulouse--meets Bilel, a French-born, high-ranking militant for the Islamic State in Syria. Within days, Bilel falls in love with Melodie, Skypes her repeatedly, and adamantly urges her to come to Syria, marry him, and do...