In the spring of 2018, the city of Austin, the capital of Texas, was under siege. A serial bomber was killing and maiming random victims with homemade devices. Could law enforcement stop the bomber before more people lost their lives? FBI agents reveal the unprecedented effort to stop the human destruction. "20 Days of Terror: The Austin Bomber" brings viewers into the investigation to see how the bureau worked side by side with multiple law enforcement agencies to identify, track and catch the bomber.