Attack on Titan, Volume 8 collects chapters 31 through 34 ("Grin," "Mercy," "Wall" and "Soldiers Dance"), picking up after the Survey Corps' expedition beyond the wall ends in disaster: Eren's squad is killed and the Female Titan gets away. Armin pieces together who among their own ranks could be the Female Titan, and Commander Erwin springs a trap that forces the reveal — Annie Leonhart, a soldier the Survey Corps trusted, is exposed, touching off a fight through the streets as Eren confronts her.
The following are series-level facts rather than specific to this volume: Attack on Titan ran in Kodansha's Bessatsu Shonen Magazine, and Kodansha's own licensing catalogue classifies it as dark fantasy, post-apocalyptic, horror and action-adventure; Kodansha Comics rates the English release Older Teen (16+) for graphic violence, which is why it is catalogued here for a young-adult audience rather than younger readers.
This edition's identifiers (ISBN 978-4-06-384712-3, language "ja") point to Kodansha's original Japanese tankobon rather than the English Kodansha Comics printing — worth a human look, as it is out of scope for this pass.