This book is best enjoyed after reading the previous books in the series. When this book opens, Cael and Ash are still healing from wounds sustained in the previous story. That said, they are finally developing the bonds that Cael has long hoped to build. Sure, they had been the closest of friends, and definitely affectionate, but it had never gone past the occasional tender kiss, or cuddling. Cael wants more, and Ash wants more, but Ash has a long history of self-loathing. 
 As a child, Ash had feelings for another boy, and a series of tragic incidences chased him far from his love and all the people he held dear. He grew up in a testing facility for cast off Therians, alongside Sloane Brodie. Ash survived the emotional and physical testing to later join THIRDS as one of the first agents in the program. He's kept his heart held tight, but now he's thinking there's one person who would keep it safe: Cael. 
 This is a definite hurt/comfort story, with both Ash and Cael working toward the kind of relationship they have always desired. In the background we have another diabolical plot hatching-one which had first come to light in BLOOD AND THUNDER but the full extent is only now being revealed. Someone has been developing a drug to control Therians in their animal form-creating drones with ultimate killing capability and no consciousness or conscience to stop them. Ash and Sloane are among the targeted, due to their history as Therian test subjects. It's a dangerous and covert business, getting control of the drug before it's used, and might put Cael in specific danger, as well. 
 I really enjoyed the careful relationship building. Just because Ash and Cael have been close for several years, Ash is stunned to learn of Cael's tragic pre-THIRDS history. Ash knows he needs to tread carefully, but it's not that long before he recognizes that he can't be the man Cael needs without taking chances on love. There's a lot of vulnerability here, and super sweet steps toward coupledom. I think THIRDS fans will be well-satisfied.