This is book ten in an ongoing series, and as such, REALLY not the place to start. While my review may not have too many spoilers about earlier books in the series, there is a whole lot of history in the books before that is required for this book to be fully satisfying to a reader. Start at the beginning with Rosemary and Rue.
After changeling knight and sometime champion of the realm, October “Toby” Daye’s adventures in the Kingdom of the Silences, there is now an actual functional cure for elf shot (poison arrows that make a pureblood fae sleep for a hundred years). Queen Arden Windermere pops up unexpectedly while Toby is hosting a slumber party for the various teens in her life. Arden wants Toby to be there while the elf shot cure is administered to the queen’s seneschal, as well as her brother, both struck down by her enemies. It needs to be done before the High King can show up and forbid them to use the cure. As it happens, they manage to wake one of two, before High King Aethlin Sollys arrives and postpones any further awakenings until they’ve had a big conclave, discussing whether the cure should be allowed, or buried forever.
Toby is ordered to appear at the conclave and is none too pleased about it. With so many different faerie rulers and high powered dignitaries in one place, it is important that Tybalt assert himself fully as the independent and aloof King of the Court of Dreaming Cats. As the Court of Cats doesn’t swear fealty to anyone, even the High King, Tybalt can’t really associate publicly with Toby, a knight to with a very set allegiance to the Divided Courts. The enforced distance hurts and unnerves them both.
As well as more faerie royals in one place for over a generation, the conclave is attended by the oldest of the Firstborn, the Sea Witch herself (and Toby’s aunt), the Luidaeg. She intends to bear witness to proceedings and brings along Karen, Toby’s honorary niece, an oneiromancer (she can walk in and interpret the dreams of others). She’s been tasked with speaking the opinions of Evening Winterrose, Toby’s nemesis, and the original inventor of elf shot. While Evening herself is sleeping through a hundred years after being elf shot herself, she wants to make sure that her case is heard at the conclave and has no qualms about emotionally blackmailing a vulnerable teenage girl to enable it.
What initially seems to be likely to be a boring few days of pureblood faeries yelling at each other, turns a lot more sinister when one of the kings are murdered and the Duchess of Saltmist is unexpectedly elf shot in her quarters. As always, when Toby starts investigating, things get bloody and fraught with several near-death experiences, taking turns for the very bad before getting better again.