I’m always inspired by Leiber’s novella, The Swords of Lankhmar, in which our favorite rascally heroes, Fafhrd and the Gray Mouser, are charged by the Overlord to protect the city’s grain fleet. In the course of doing so, they learn a great deal about the society of the rats of Lankhmar, who pull many strings in the city.
Fun fact: The Swords of Lankhmar was a big inspiration on my Torchbearer adventure, The Secret Vault of the Queen of Thieves.