The Library Trail by M. L. Buchman

When the person you depend on most disappears, where do you begin the search?

Her mentor, an ex-spy turned librarian, vanishes without warning. Dilya and Zackie, the former First Dog, can’t find her on their own. Before it’s too late, they must reconstruct a trail of hints left in keeping with Dilya’s inner circle of friends.

But when hints turn into solid clues, Dilya knows they must hurry or they’ll be too late.