In the line of duty, Mackenberg was ordained by so many Spiritualist churches (always for a fee), that her nickname in the Houdini organization was “the Rev.”

Mackenberg’s most newsworthy case came in 1926, when Congress was considering a bill to outlaw fortunetelling in Washington. Public hearings became chaotic as people made competing claims on the validity of divination. Houdini, a star witness, shared the results of his investigations into spiritualism, calling mediums “mental degenerates” and cross-examining professional psychics himself.

Mackenberg, for her part, testified about her recent undercover experiences visiting Jane Coates, a notable Washington medium. In an article included in a 2016 anthology about Mackenberg, compiled by Tony Wolf, she recalled, “It was my testimony, brief and pointed, that touched off the rockets and pinwheels and giant crackers of startled emotion when wrathful persons broke in with protestations and shouts of ‘That’s a lie!’ and ‘We never did such a thing!’”

Her bombshell: She said that Coates had confided to her that the proposed legislation would never be passed because her customers included four senators and because “table tipping séances are held at the White House with President Coolidge and his family.” Coates denied the allegations, The New York Times reported at the time, noting, “Today’s session was unusually disorderly and came near winding up in a free-for-all fist fight.”

Rose Mackenberg was born on July 10, 1892, in Brooklyn to Lewis and Anna Mackenberg, immigrants from Russia. As a young woman she worked as a stenographer in a law office and as a private detective. When a banker asked her to look into a medium who had advised him to invest in a stock that proved worthless, she consulted Houdini, who was already famous for his crusade against psychic swindlers. He advised her on how to uncover the fraud, and then recruited her to join him.

After Houdini died unexpectedly in 1926 at 52, Mackenberg continued their work, taking on clients that had an interest in combating fraud, including police agencies, insurance companies and Better Business Bureaus. She gave lectures on how to spot a phony psychic and revealed the theatrical tricks she had seen hundreds of fake mediums employ in darkened rooms (hidden harmonicas to produce ghostly noises, for example).

She also wrote numerous newspaper and magazine articles on the topic as well as an unpublished autobiography, “So You Want to Attend a Séance?” A 1949 Hearst syndicate article described her as “perhaps the only woman ‘ghost-buster’ in the world.”