 In an expedition to Shinganshina , the Scouts are attacked by a Female Titan who attempts to capture Eren . Although the Scouts are able to briefly capture the Female Titan , she breaks free and devastates Levi 's squad , forcing the expedition to retreat . Armin determines that the Female Titan is Annie , one of the cadets who taught Eren to fight , and devises a plan to capture her at Stohess . During this operation , collateral damage reveals that Titans reside in and make up the walls surrounding the human settlements . 
