The Library Trail — M.L. Buchman / Matthew Lieber 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.