Characters: see previous summaries in series
This book picks up right where Onyx left off, with Dawson back home living with Daemon and Dee.
Katy and the gang go back to school after a large snowstorm, giving them time to recoup from everything that's happened recently, and Katy sees someone she thinks is Blake. It does turn out to be him and he confronts her telling her he needs the Luxen's help and hers to try to get his friend Chris from Mount Weather because he's afraid they will kill Chris since Blake's mission to bring Katy back failed. Katy goes cuckoo for a minute and attacks Blake saying she will never help him since he killed Adam and almost killed Dee, but he tells her he can help get Beth back because she's being held captive there too.
After discussing with the rest of the Luxen, they all decide they have to at least try for Dawson's sake, because if they don't he's going to go back for her anyways.
Blake takes them to a club that his friend Luc owns, who is a hybrid also. Luc is very familiar with Mount Weather's security system, so he makes a deal with Daemon and Katy that as long as they promise to provide him with a favor of his choosing the next time he needs it he will shut down the security systems for a 15 minute window and get them all the passwords to the doors.
The Luxen and Blake run the attack on Mount Weather like freakin ninjas and everything is going awesome, but when they get to one of the doors they are sprayed with airborne onyx and Katy and Andrew both collapse.
The plan has failed, but Blake tells them a story of when he was at Mount Weather training with Daedalus about how everything the trainees touched seemed to be coated in onyx, and he thinks it's so a resistance can be built up. He says if they train with the onyx every day they may be able to defeat the airborne system. They all agree to do so.
In the meantime, although Katy still feels hatred for Blake for what he did, she does also feel sympathy in knowing that he did what he did to try to protect his friend, the same as she would if it were Daemon or Dee.
Although she and Dee aren't best buds anymore, the do try to mend their friendship by going prom dress shopping together and trying to have a few heart to heart's.
On a side note too, Katy keeps having dreams that Daemon comes into her room and sleeps with her (just sleeping, not the other thing you pervs), but it turns out it was Blake who actually WAS lying down with her. She realizes this when he leans in to tell her something in the classroom one day and she smells his cologne....the same scent she smells when she had been "dreaming".
Not too long after, Katy comes home and Carissa is in her room, but she's gone totally loony and been turned into a hybrid and tries to kill Katy. After expending her Source, Carissa spontaneously combusts (the result of an unstable hybrid) and a few days later while searching for her shoes under her bed Katy pulls out a rock that turns out to be opal (ta-da! hence the title) and is an extra bit of protection against the onyx.
Will shows up back at Katy's house, but his cancer has come back with a vengeance and Katy easily kills him when he shoots her.
They try another attack on Mount Weather and everything seems to be going great. Beth and Chris are there, both seemingly mistreated but sane, but when they begin to head back out, laser grids start shooting across the room and Arum are chasing them. Katy sees Blake and sees him holding the opal. Realizing he stole it from her, she knows he has sounded an alarm and that's why everyting is going nuts. He gets away from Katy and the other Luxen, but Katy gets stuck between a laser wall and the rest of the group. They have to leave without her, although Daemon swears he will be back soon to get her, then the Arum come up and knock Katy out.
End of book 3.