Alcatraz Versus the Knights of Crystallia — Brandon Sanderson

WHEN ALCATRAZ and Grandpa Smedry make a pilgrimage to the Free Kingdom city of Crystallia, the Smedry home base, Alcatraz is shocked to see that he is a legend. When he was a baby, he was stolen by the Evil Librarians -- and his mother, a Librarian herself, was behind it. Now, with his estranged father, who is acting strange; his best friend, Bastille, who has been stripped of her armor just when they need a good knight; and Grandpa Smedry, who is, as always, late to everything,

ALCATRAZ TRIES TO SAVE A CITY UNDER SIEGE.
FROM WHOM?
WHY, THE LIBRARIANS, OF COURSE!

And, in particular, an especially evil Evil Librarian who has followed the Smedrys to Crystallia in hopes of shattering the city: Alcatraz's very own mother!

In this third book in the Alcatraz Smedry series by acclaimed fantasy writer Brandon Sanderson, it's up to Alcatraz, a boy with all the wrong Talents, to save the day!