Okay so a comet or something weird hits a city and all physics within the impact zone are crazy. Hard Science fiction but with a 50's style detective. Going into the "whacky physics" zone is prohibited but there are guides willing to take tourists. The cover has cats and playing cards because all these black cats come out on the fringes of this area. Super weird story but with poetic prose and the irony is that some people are from the area but aren't quite human.... Driving me crazy, can't remember!
It might be M. John Harrison's 2006 novel Nova Swing.
from the Amazon link:
Not far from Moneytown, in a neighborhood of underground clubs, body-modification chop shops, adolescent contract killers, and sexy streetwalking Monas, you’ll find the Saudade Event Site: a zone of strange geography, twisted physics, and frightening psychic onslaughts. Vic Serotonin is an illegal “travel agent” into and out of Saudade. His latest client is a woman as unpredictable as the site itself—and maybe as dangerous. She wants a tour inside Saudade just as a troubling new class of biological artifacts have started leaving—living algorithms that are transforming the “real” world in unsettling ways. Pursued by a detective intent on collaring him for his illegal tours, and hunted by a gangster convinced that the travel agent has infected him with a rogue artifact, Vic must make one final trip as the universe around him rapidly veers toward viral chaos.