Attack on Titan Volume 1 by Hajime Isayama
Humanity hides in a walled-off territory from the Titans, gigantic humanoids. The walls have preserved security for a hundred years but a new threat arrives in the form of a colossal Titan, taller than the wall and powerful enough to destroy it. After he breaches the wall, other Titans swarm in and eat people. The remaining humans retreat into the area of a second wall (there's a third wall also) with five years of relative peace. The Titans don't come back; occasional survey teams go out and try to drive back the Titans. Those teams have always failed.
Eren and Mikasa are two youths who witness the attack and the death of Eren's mother. They are trained to fight and after graduation have three choices. They can join the Garrison, which reinforces the walls; the Survey Corps, which takes the fight to the Titans; or the Military Police Brigade, which maintains order within the walls. This year's graduates debate about which branch to join. The MP Brigade provides the safest life. The Survey Corps paradoxically provides hope to humanity that they might overcome the Titans, if the Corps can ever find a way to win. The Titans have only one vulnerability--a brutal blow to the back of the neck that will stop them from regenerating (even if their heads are shot off by cannon fire, they regrow in a few minutes). As the graduates have one last celebration together, the colossal Titan appears again and they are forced into action before they can even get settled into their new life.
This manga is the basis for the hit anime show and seems to anticipate it. The volume is divided into four "episodes" that have titles similar to four of the first five episodes of the television show. TV episode three, about life in the training corps, is an addition. Maybe the manga will have a flashback to training in a future volume? Otherwise, the story is identical.
The action in the manga is a little hard to follow at times. The battle tactics aren't immediately clear. The art does a good job of showing the scale of the Titans and the horribleness of their eating people. I found the anime easier to follow, except for the exposition about the walls that flashed by too fast. And the anime is more visceral. The music and vocal performances add a bit extra to the story.
I found the manga intriguing but I'm going to stick with the anime version for the rest of the story.