Another lengthy trip means another Terry Pratchett novel to pass the time (at the gate and on the plane) reading. And Pratchett's comic fantasies are exactly what the doctor recommends… to get into the right, good mood for a vacation.
Guards! Guards! is the first full length feature of the Discworld's City Watch. It is the first detailed description of the inner workings of Ankh-Morpork and its political arrangement. And, accidentally, it was the first Pratchett novel that I actually bought myself, back then when I still read my books in the German translation.
Already the way the City is run makes the novel well worth reading it. The Patrician is just such a brilliant character.
Incidentally, there is again an annotation available. Some of the finer details may be easily missed otherwise.