This is an unpublished (unsubmitted) book that Myka's father believed had been destroyed a long time ago, at his behest and by his wife, when he found himself unable to part with the book; also due to fear of it being rejected by the publishers. The book seemed to have been an obsession of Warren's or something that was destined to be, because, no matter how many times he tried to write a different story, he would always end up writing the same novel. The book appeared to mirror his own life, or rather the relationship he wanted to have with Myka, but had been unable to achieve. The book was ultimately spared destruction when Mrs Bering couldn't bring herself to burn it, and instead hid it away, never knowing that it would eventually save her husband's life.
Many years later Warren's life was placed in danger (possibly by James MacPherson) when the notebook of Edgar Allen Poe found its way into his possession. Panicked and disoriented due to separation from its companion artifact (the pen), the notebook attached itself to Warren when it sensed his love for the written word and also his strong creative spirit. The two separated artifacts then used him as a means of communication with one another, and Artie explained that, unless something was done quickly, Warren only had 48 hours at most to live.
Artie suggested that Myka read to her father in order to keep him rooted in reality, and improve his chances of survival, while Claudia and Pete went after the pen, which was causing trouble with its own endeavors to be reunited with its partner. Myka tried almost every book in her father's shop, but nothing seemed to work and her father slipped further and further into the notebook's grip. Artie told the distraught agent she had to find a special book, one that meant more to her father than anything else in the world, an instruction which caused her to remember the book that her mother mentioned earlier while they were looking after Warren.
Retrieving the book from its hiding place, Myka began to read the Blue Willow Sky to her father, while obviously being herself quite moved by what the book was about. The emotional content of the book and its passion had the effect of calming the distressed artifact, mostly likely because the content reminded it of its old master. The link the book had with the pen also ensured the pen was able to hear the story as well, and it too calmed down enough to leave the person it had chosen as its own substitute, allowing Claudia and Pete to snag it and bag it.