The Castafiore Emerald (The Adventures of Tintin)
The Castafiore Emeraldwas Herge's third-to-last completed Tintin story, and the most unconventional.  Rather than a globe-trotting adventure, it takes place completely at Marlinspike Hall, where an incapacitated Captain Haddock is being nursed back to health by an unwelcome visitor in the form of Bianca Castafiore, the "Milanese Nightingale" who then suffers a devastating loss ("Mercy, my jewels!").  It's disfavored by some fans due to the lack of action, but the locked-room mystery, character interactions, running gags, and crazy Calculus inventions keep it fun and definitely worth reading.--David Horiuchi