Strange the Dreamer by Laini Taylor

Lazlo Strange is a foundling who has grown up alone and unloved, sustained only by his fantasies and stories of a city known as Weep. As an adult, Lazlo finds his way to the Great Library of Zosma and becomes a librarian, tasked with supporting scholars in their work. Eril Fane, the liberator of Weep, pays a surprise visit to Zosma. Lazlo seizes the chance to join an expedition to the city he has dreamed of for so long, and he is caught up in an old conflict between Weep's mortal residents and blue godlike beings who had terrorized the city until Eril Fane slew them. Unbeknownst to the inhabitants of Weep, five children of these magical beings have survived and live in the giant seraph that hovers over the city. When Sarai, one of these Godspawn, visits Lazlo in his dreams, their growing relationship leads to the revelation of long-hidden secrets and opposition from other Godspawn, who desire revenge on mortals. Read a sample.