Ubik by Philip K. Dick

Set in a futuristic world, the novel follows Joe Chip, a technician at a psychic agency, who becomes trapped in a reality-altering phenomenon after a mission on the Moon goes wrong. As his reality begins to unravel, Chip and his colleagues find themselves in a bizarre world where time seems to be moving backward and a mysterious product called "Ubik" appears to be the only thing that can save them. The book explores themes of reality, entropy, and human perception in a surreal and often humorous manner.

The 802nd greatest book of all time