I kinda wish I'd read this one before I read Mating Challenge, since it really sets up some helpful background and makes Aiden a much more sympathetic character (and makes me believe that Nia isn't quite so forced into the mating thing). But sadly, I didn't... I haven't read Mating Season yet though, so at least now I have some of the background between Tristan and Nikita going in.
This was a pretty okay book. It happens right before Mating Challenge, as Aiden is trying to get Nikita to set a date for the challenge and we're introduced to the fact that Nikita is actually a twin and it's Nia that Aiden has been lusting after. Nikita in the meantime is having dreams of a past-life and the lover she had then while she remains in hiding from the Silver Wizard, who prophecy says will take her back to the Tir-na-nog when she turns 25 (soon). Tristan already knows where she is and wants to get to know her a bit by turning into a puppy and getting close to her. That's all that really happens here, but we do get the flashback scene of Nikita's past life with the man, who is presumably Tristan. So I definitely recommend reading this for background on the upcoming books, but it's not really necessary to completely understanding them (at least Mating Challenge...don't know yet about the next one).