Hidden Hero, Book 3 of the Ancient Court Trilogy: A Hidden Novel #9 (PB) (2017)

A hero can come from the unlikeliest of places...

After a year-long separation and a search across continents, Macy and Nic have found each other again. Now they must find her family--the birth mother who abandoned her at the hospital and fled back to her people's secret sanctuary--if they are to beat the clock and save the human race from the onslaught of the coming Plague.

Alessia didn't intend to activate the deadly virus, but after determining that Nic betrayed her, she's almost glad she did. The only problem? She won't be around to enjoy the aftermath--she's being held captive on a remote, windswept island by a mysterious guy who's completely immune to her Sway and won't let her get close enough to use her deadly glamour on him.
Give in to the Glamour once more as the end of the human world looms, an ancient secret is unearthed, and a hidden hero emerges.