he went out to walk the dog. Excellent neighborhood. Broad daylight. People everywhere.

In a city of infinite prescribed routines, it doesn't get any more unexceptional than that.

And then she never came back.

There was nothing particularly conspicuous about Svetlana Aronov when she set out Monday afternoon to walk Bim, her father's 1-year-old cocker spaniel. She wasn't dressed up. That wasn't her. She might have been smiling, because she was quick to smile. Just that morning she had had a mole that displeased her stricken from her cheek, a vanity thing, but something she was happy about. She couldn't have gone far, because she had a busy day. And then the threads run out.

And so three days later, her family and the police are devoid of clues or plausible theories. There has been no ransom demand. Her husband, Alexander, said he could not name a single enemy who would want to harm her. By now, he has heard every conceivable plot whispered on the television news, down to, could it be the Russian mob? "Nothing makes sense," he said yesterday at their apartment on York Avenue, between East 63rd and 64th Streets. "It's as good an idea that she was taken by a U.F.O."

Polina, the older of their two daughters, said, "She like fell off the planet."

In a city where bizarre is almost without meaning, the case of Ms. Aronov, 44, ranks among New York's most improbable vanishings, with echoes of Judge Crater and Etan Patz. A police bloodhound traced the scent of the dog to 68th Street and York Avenue, where it ended. That's about as congested a corner as Manhattan offers. Memorial Sloan-Kettering Cancer Center occupies one side of the street. Rockefeller University and New York Weill Cornell Center are across the way. If she was abducted, how could no one have seen anything suspicious? Why would anyone risk such a chancy crime? And why take the cocker spaniel?

"The fact that she left her apartment, leaving behind money and jewelry, and apparently took her dog for a walk in broad daylight and did not return," said Chief Michael Collins, a Police Department spokesman, "was highly unusual."

Investigators confirmed that her husband, an internist and hematologist, was in his Brooklyn office when his wife disappeared around 2:30 p.m. While the police always look first to the husband or wife, one investigator said, "There is nothing to move him to the top of the pile."

Dr. Aronov said he did not realize anything was wrong for nearly eight hours, because his wife had scheduled one of those impossible but all too familiar New York days. It involved cosmetic surgery, a child who had to be picked up by her husband's stepmother, keys to be left with a doorman, a trip to the airport to get her father and drive him to Southampton. And, of course, the dog.

Alexander Aronov and Svetlana Byzov were childhood sweethearts. They grew up in St. Petersburg, Russia, fell in love and were married there almost 25 years ago. He called her Sveta. She called him Sasha. They moved to Canada, where he went to medical school, then finished his studies in Italy. He moved to New York for his residency in 1989, and she followed a year later.

Dr. Aronov, 45, has offices in Brooklyn and Manhattan. Ms. Aronov helps him with the books and has her own part-time business, dealing in the specialized world of avant-garde Russian books from 1910 through the 1930's. She also collects porcelain plates.

Last April, her parents, Anatoly and Lilia Byzov moved here from St. Petersburg, and settled into the couple's country house in Southampton, on Long Island.

Friends described her as warm-hearted, highly cultured, athletic. She and her husband are avid skiers. "She is interested in everything the city could offer," said Olga Dolgicer, one of her best friends. "She would not hesitate to help a stranger. Her house is always full of friends."

Dr. Aronov said she was not troubled and he could not imagine her deliberately vanishing. "It sounds sentimental, mawkish," he said. "But our life was like an American dream." Tomorrow, they were to leave on a 10-day ski trip to Italy.