21. The Hostile Hospital by Lemony Snicket

ISBN 0060288914 - HarperCollins, 2001
This is a pivotal book in the Series of Unfortunate Events. For starters, it begins exactly when and where the previous volume, The Vile Village, leaves off. The subsequent books do the same and you are left with a "cliff hanger" at the end of each one.
Count Olaf is heard but not seen as the voice of "Mattathias" over the hospital's intercom. He appears in the final scene but not in disguise. In previous books he takes great pains to obscure his distinguishing features - single eyebrow, shiny eyes, tattoo of an eye on his ankle. From here on, he no longer takes on false identities.
Mr. Poe does not appear in The Hostile Hospital and the Baudelaires have no official guardian.