Many millennia ago, ten angels from Heaven betrayed their kind. Each helped the Devil (also known as Lucifer) in one way or another and all ten were banished and made the nine day and nine night fall to Earth. Once on Earth, five of the fallen angels' wings turned black as they went to seek out Lucifer, but the other five regretted their actions and stayed far away, their wings remaining white.
Nowadays the five 'good' fallen angels - Averia, Leora, Hope, Isobel and Diva - call themselves the 'Guardians', even though they were labeled by the true Guardians as the Betrayers. They move from place to place, sometimes helping humans in big or little ways, keeping their immortal identities secret and emotions detached from all mortal contact. They were left alone by Lucifer's angels for thousands of years, but now Jasmine, Destiny, Zara, Verity and Savannah are back - and still doing Lucifer's dirty work. Averia says so herself; the only difference between the Guardians and Lucifer's angels is the fact that the Guardians still have hearts. Lucifer's angels want to recruit to the others, in the hope that Lucifer will finally overthrow humans. They also believe that Lucifer still has some power over their other fallen sisters...
When the Guardians move to London, the angels meet five attractive but untimely lads named Liam, Harry, Niall, Zayn and Louis. Why are they untimely? Because Lucifer's angels have started following the Guardians, and with Lucifer himself after them too, the angles have to be on the top of their games.
So what happens when all of the angels let their hearts get in the way?