Spoilers ahead for the first five volume.
As in, they arrive at the magical city (underwater!) with Qiffery seriously injured, there is an investigation into the disappearances of the last volume (with our main characters remaining discreet about some details), and discussion with one of The Wise about what to do about the test.
They are told that if they astound him with their magic, they will have passed the test -- all four of them, even though only Richeh and Agott were taking the test.
The tale involves the plot thickening, with another character taking interest in Coco; Coco's realizing how little she knows about Qiffery's motives; rainbows; markets that sell trinkets; a surprising side-effect; how blase an experienced witch gets with magic; and more.