Ms. Schembri fell into the investigative profession almost by accident. After graduating from Hunter College in 1980 with a degree in economics, she worked for New York City as a tax investigator , specializing in real estate cases . After five years , she was ready to try something new.

While looking up records at the courthouse , she ran into a friend of her husband who was working for a private investigation group . He had been hired by a congressional committee to investigate Ferdinand Marcos , then the president of the Philippines, and his family’s real estate holdings in the United States .

“They had all these documents, but they didn’t know what they were looking for,” Ms. Schembri said. So she took a week’s vacation , went to Washington and locked herself in a room with the boxes . She said she came out with proof that the Marcoses owned four high-rises in New York , and with a new career.

Ms. Schembri said she was initially drawn to the painstaking — what some might call the mind-numbing — labor of investigation. She loved sorting through page after page of documents and records, searching for that ne edle in the haystack .

“I told them I didn’t want to do cloak-and-dagger stuff,” she said.

But when she did start to do the surveillance and tailing and subterfuge traditionally associated with the trade of a professional snoop, she said she was surprised by how good she was at it.

A spy’s job depends on the ability to make herself invisible, to inhabit the background of someone’s day. It’s a skill Ms. Schembri seemingly perfected. With a change of clothes and the swap of a wig, she could transform herself from a downtown punk to an uptown dame. She could sometimes cycle through several personas a day , adding and removing glasses or a hat, shedding a jacket to unveil a bright top, peeling that off to reveal a plain T-shirt .