Pynchon's second novel, The Crying of Lot 49, is short, witty and relatively accessible—but, even so, the plot is too elaborate and absurd to fit into a brief summary. It features an ancient, underground mail service known as the "Trystero". His most famous novel is his third, Gravity's Rainbow, published in 1973 to widespread critical acclaim and winning the 1974 National Book award. Set in Europe at the end of the Second World War, Gravity's Rainbow combined and elaborated on many of the themes of his earlier work, including paranoia, conspiracy, synchronicity, and entropy.  (Source)