Backstabbed in a Backwater Dungeon: My Party... (Manga) Vol. 03

Light and company find their adventuring interrupted by reports of suspicious killings in the very same dungeon they're crawling. Tempted by the prospect of boosting his rank—not to mention the generous reward promised by the Dagas Adventurers' Guild—Light sets off to catch the killers. 

The hunt takes a personal turn, however, when a party of innocent young adventurers gets slaughtered in the crossfire. Light's quest for vengeance will have to wait as he turns his wrath on a new target!

Full Title: Backstabbed in a Backwater Dungeon: My Trusted Companions Tried to Kill Me, But Thanks to the Gift of an Unlimited Gacha I Got LVL 9999 Friends and Am Out For Revenge on my Former Party Members and the World (Manga)