National Geographic World's Most Dangerous Gang: You've spotted the graffiti and seen their tattoos. And you've read the shocking headlines documenting their brutality. But what is driving the rapid spread of the ultra violent gang MS-13, which has infected big cities and small towns across the country. Lisa Ling takes you deep inside a merciless world hidden in plain view. Through revealing interviews with active members, National Geographic reveals the extreme culture and rituals of the MS-13 gang.