Goblin Slayer, Vol. 5 (manga)

"On their mission from Sword Maiden, Goblin Slayer and his party find themselves ambushed by a horde led by a goblin champion! As imposing as this threat is, though, it can't remotely prepare the adventurers for the demonic familiar they are shocked to discover guarding the goblins' secrets ... What fresh horrors dwell beneath the water town?"--Back cover.