Light of the Stygian Orb. The Invisible Entente, #5

As an archer who is deafblind, sixteen-year-old Molly Harris has always lived an exceptional life, but since rescuing the angel-demon hybrid Zachariel and being introduced to the otherworld, she's craved a different kind of extraordinary. On her mission for answers, however, Molly realizes the road to the truth is more treacherous than she expected. Zachariel is a freak of nature who has never fit in anywhere, and he's grown comfortable with his solitary existence.
Now, not only does he have a nosy teenager invading his personal space, he's also dealing with a shady demon who wants to recruit him for a secret project - and who won't take no for an answer. As Zach delves into the demon's scheme, he discovers he's an unwilling pawn in a life-or-death game. Zach and Molly may be an unlikely team, but it rests on them to hold back the threat that could shake the foundations of the world.