All of the weak monsters have gone into hiding since a leader of the devil king's army has settled in near town. Kazuma, who had been focusing on improving his skills, is stuck at a standstill. With nothing else to do, Kazuma tags along with Megumin's training, which consists of unleashing explosion magic into an abandoned castle.

With debt looming over her, Aqua convinces Kazuma to accept a high difficulty quest to purify a lake, which doesn't require killing any monsters.

Dullahan, a top leader in the Devil King's army, yet again appears at the city in a frenzied rage.

Kazuma and Aqua can't properly accept rewards from quests due to their mediocre party lineup, and are so destitute that even keeping wood on the fire is difficult. Kazuma comes up with a plan and visits a magical accessories shop run by a woman called Wiz.

Kazuma and the others manage to lure the kite hawks into a cave and deal with them all at once, only to cause more trouble for the other travelers later when Aqua attracts some zombies.

The party makes their way to Arcanretia, a city known for it's recuperative hot springs! But what they don't know about the city might spell doom for their vacation.

Evading the angry mob, the gang discover that the source of the town's water is being poisoned by the man from earlier, who is revealed to be one of the Devil King's army leaders, Hans the Deadly Poison Slime.