The Angel By The Tower - The Keeper Chronicles, #1

Gabriel wakes up naked and alone in the desert with only one clear memory-he must find Abby Campbell before it's too late.  Normally it wouldn't be a challenge-he is her guardian angel after all.  Unfortunately, a dispute with his heavenly Boss has left him busted down to a mere mortal with no wings, no powers, and no idea of exactly what he's supposed to protect Abby from.  Once he convinces Abby he's not completely bonkers, they work together to find the key to a mysterious tower and the ancient evil locked inside.  But the answers force Gabriel to choose between saving Abby and being exiled from Heaven forever.