This contains three different stories, each between 150 and 180 pages long, which were written over the course of 7 years, so it's a collection. There are certain gaps between the end of one and the start of another, though it's a few months at most.
The stories revolve around Nita and Kit, who both came across How-To manuals for being a wizard. They each agreed to take the Oath, and this puts them in various situations where they have to thwart the Lone Power, the one who introduced Death in all its forms into existence. Wizards are supposed to work to slow down the ultimate death of the universe (via entropy) however they can. But the Lone Power wasn't happy being booted out, so they keep running up against it.
The plots are generally entertaining, although the third story took a long time to get anywhere. The problem there was it was Nita's little sister undergoing her Ordeal after rather blithely accepting the Oath, and so you knew she was on some sort of important mission, but it was quite a while before the mission became clear. Powers moving in mysterious and ambiguous ways, I guess. Deep Wizardry, which was the second story, was my favorite of the bunch. That may be because a Master Shark is prominently involved. You make a key character that is an ancient, massive, predatory shark, one which can command and control all other sharks if it wishes, and I'm probably going to dig that.
I did have some issues with certain aspects of the philosophy involved. There's a quote before one of the stories, supposedly from the most powerful resource in their world that says 'Those who refuse to serve the Powers, become the tools of the powers. Those who agree to serve the Powers, Themselves become the Powers.' I can't say either of those options sounds palatable to me, and I'm never a big fan of fictional universes where abstract concepts start jerking people around like puppets on strings. I prefer the idea that one gains (or unlocks) the power, then uses it for good because they choose to, rather than because some unknowable force is just going to twist them into doing so if they don't, or punish them for refusing. We're told if a wizard breaks the Oath, or won't complete a task, they are stripped of their power and memories of anything related to wizardry.
At one point, Nita is contemplating not carrying out something she promised to do, she's told that the ritual she's supposed to participate in will fail, and so she'll contribute to the that-much-sooner death of the universe, and she'll carry a nameless sorrow in her soul for the rest of her life. Which is fucked up enough, but then the character explaining the stakes to her says, that's not so bad, lots of people think going through life with a nagging sorrow in the bottom of their soul is natural.
To say I disagree would be an understatement. I can't buy that even if people do feel that, they think it's natural. And the fact the Powers would drop that sort of bomb on someone for being unwilling to die for their goals, strikes me as an extremely petty move to make. The Powers remind me of the NCAA: They try to take all the credit and all the benefits of what the wizards/athletes, and if said wizard/athlete tries to step outside the bounds the Powers/NCAA establish, try to act in their own self-interest, that brings down the hammer. Any system that reminds me of collegiate athletics is not a system I'm going to be fond of.
So that was an ugly undercurrent to the last story and a half of the book. The first story and a half were good, though.