The facts are at once grotesque and gripping. In an apartment building in one of the city’s most expensive neighborhoods, two lawyers were raising fighting dogs more accustomed to chain-link fences than stylish entry gates. Frightened neighbors bought pepper spray and mailmen braced for trouble. Then, late last week, the two 100-pound dogs broke loose from their female owner, bounded down the hallway and killed a 33-year-old college lacrosse coach in her doorway.

The New York Times reported that the hallway blood bath was so horrific that police officers at the scene had to receive trauma counseling. The case has taken complicated twists and turns since then. There are links to a white supremacist currently doing jail time, a prison-based gang known as the Mexican Mafia and a brutal attack-dog training network. The city’s prosecutor has assigned 40 investigators to the case.

All of this has unleashed the primal fears of half the city’s population. That’s because the real faultline in San Francisco runs between dog lovers and dogless neighbors: those of us who get nervous at the sight of pets without painted toe nails or bows in their hair. San Francisco is home to dog-friendly restaurants, doggie day camps, dotcom doggies who “work” in loft offices. It sometimes seems half the people in the city carry around plastic bags at lunchtime that don’t contain anything you’d care to eat.

The rest of us have fear. For us, the attack has turned the city into a mongrel minefield. Every collie is a potential Cujo. Every wagging tail a metronome-ticking, chest-pounding fright. I’ve been skittish ever since a run in with a bulldog three weeks earlier, but when I step outside for the first time since the mauling, like a Pekinese, I am unusually high strung. I spot my first enemy bobbing toward me: mottled coat, deep brown eyes and all-business snout of a German Shepherd bred with a wolf. As he growls and speeds out on his leash, I duck for cover. His owner reassures me: “He just likes your pants.” So do I. And both of my legs.

That night, a pair of docile Golden Retrievers outside a Cole Valley wine bar scare me off the sidewalk and into the street. They’re not awake, but they could be. And I don’t want to take any chances. On my morning walk, I avoid all dogs, even small ones, but I’m not embarrassed. Half the city, it seems, is turning tail.

A few blocks from the attack in Alta Plaza park, strollers and bikers give dogs wide margins, their tongues wagging over the tabloid developments in the case. Professional dog walkers grit their teeth, hounded by grating comments like “Oh, good, those are small dogs” when their pint-size charges hit the streets.

A young woman says she’s “very careful” when she walks her twin 10-month-olds-babies, not pets. While on their Pacific Heights routes, UPS men deliver confessions: “I do get nervous,” a veteran driver admits. Miles from the attack, over the whir of dryers, paying customers at Noe Valley’s V.I.P. Grooming come clean about the new fear. “Unleashed dog, unleashed dog!” mocks one groomer, of the criticisms she’s ignored while walking her own dog this week.

Around the corner, a nervous pet owner muzzles her puppy at the Noe Valley Pet Shop even though she insists the nine-month-old Schnauzer is not an aggressive pet. She’s doing it because he makes people uncomfortable. “And I guess he sometimes jumps on kids,” the clerk admits.

Catnip and Bones, an animal boutique in the Marina, seems to be one of the few places in the city where there is little concern. “It’s not as if some happy fluffy dog went berserk on someone,” a Springer Spaniel owner says, and then repeats a popular dog owner phrase: “There are no vicious dogs, just bad owners.”

Dogma to half the city. Doggerel to the rest.