The Dark Mirror By Samantha Shannon

Paige Mahoney is outside the Republic of Scion for the first time in more than a decade – but she has no idea how she got to the free world. Half a year has been wiped from her memory. As she makes her way back to the revolution, her journey takes her to Venice, where she learns a dangerous secret – one that could change the face of the war between humans and immortals. Before she can return to London, she must help the Domino Programme unravel the sinister Operation Ventriloquist. And it soon becomes clear that the one person who could recover her memories – Arcturus Mesarthim – might also hold the key to saving Italy.