Darkness, Aqua, and Megumin are back to continue their quest against the Devil King. Kazuma is back too, but the only adventures he has waiting for him exist within the criminal justice system. Finding no support from his allies, Kazuma is arrested for treason due to accidentally blowing up a noble's mansion.

As Kazuma notices that Darkness hasn't come back since negotiating with Alderp, Megumin brings in a cat that she names Chomusuke.

Wanting to earn some real money, Kazuma and Aqua go to explore a newly discovered pathway in Keele's Dungeon, coming across gremlins, mimics, and the undead along the way.

Darkness suddenly returns, asking for the others' help in getting out of an arranged marriage with the Alderp's son, Walther.

As a result of a magic circle that Aqua had drawn in Keele's dungeon, strange explosive doll monsters have started to appear, putting the town at risk.

Kazuma is surprised to discover that Vanir had an extra life and has since quit his position as a commander to work at Wiz's shop, striking up a business partnership to sell products from Kazuma's world.

Vanir gives Kazuma the choice of either selling the intellectual rights for his real world products for a one-off payment of 300 million eris, or maintaining a profit-sharing contract of 1 million eris a month.

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 travellers later when Aqua attracts some zombies.

After witnessing Aqua warp the town's citizens with her petty confessional hearings, Kazuma takes a dip in the mixed bath, where he comes across another man who is as sick of the town's behavior as he is.

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.