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The Exchange Principle: An Edwardian Mystery Featuring Margaret Harkness
Unravel a murder, uncover a legacy.
A scientist desperate to prove his theory… A journalist newly arrived to help him… A murderer unaware of “the exchange principle,” where every contact leaves a trace…
Journalist and part-time investigator Margaret Harkness steps into the smoky, intrigue-laden world of 1912 Lyon, France, and witnesses the birth of forensic science when Edmond Locard, a man inspired by Sherlock Holmes, struggles to prove his “Exchange Principle.” Every contact leaves a trace, he insists.
When a body is discovered in the opulent parlors lining Lyon’s back streets, Margaret and Locard employ nascent forensic methodology, striving to demonstrate the veracity and effectiveness of his Principle to skeptical judges and juries.
Can Locard and Margaret catch a killer by deciphering the vestiges of evidence left behind, or will this clever murderer slip through their fingers?
Based on true events and characters, The Exchange Principle is a story of unexpected connections and lasting impact in which the events of 1912 Lyon are told years later in post-war Florence, Italy. A final diary entry and an unexpected meeting reveal the imprints that Margaret Harkness herself will leave behind, a testament to the enduring power of human connection.
“A tale of science, suspense, and the indelible marks we leave on each other.”
– Derek McFadden, author of What Death Taught Terrence
"A top of the table forensic mystery with a real life forensic detective!"
– Advance reader review
Margaret Harkness (1854–1923) was a trained nurse, journalist, and writer (as John Law) of several notable books, and was an independent woman who passionately advocated for the disadvantaged. “In her works of social investigation, Harkness uses a tone of social realism or naturalism, making her different from her male contemporaries.” (Deborah Nord, Walking the Victorian Women, Representation, and the City. Cornell UP)
Enjoy more stories featuring this remarkable woman interwoven with real-life events by Bradley Harper.
A Knife in the Fog (novel)
London, 1888. Professor Joseph Bell and a young Arthur Conan Doyle join the hunt for the gruesome murderer soon to be known as “Jack the Ripper.” Margaret Harkness, local to the East End streets of Whitechapel, might just prove to be an indispensable ally.
Queen’s Gambit (novel)
London, 1897. Margaret Harkness accepts a plea for help when her old friend and comrade, Professor Joseph Bell invites her to join him on a secretive mission. But she soon finds herself in an assassin’s crosshairs bent on two both her and Queen Victoria.
The Exchange Principle (short story)
Lyon, 1912. Margaret Harkness steps into the smoky, intrigue-laden backstreets of Lyon, France and witnesses the birth of forensic science when Edmond Locard, a man inspired by Sherlock Holmes, struggles to prove his “Exchange Principle.” Does every contact leave a trace? Or will a clever killer slip through their fingers?
A scientist desperate to prove his theory… A journalist newly arrived to help him… A murderer unaware of “the exchange principle,” where every contact leaves a trace…
Journalist and part-time investigator Margaret Harkness steps into the smoky, intrigue-laden world of 1912 Lyon, France, and witnesses the birth of forensic science when Edmond Locard, a man inspired by Sherlock Holmes, struggles to prove his “Exchange Principle.” Every contact leaves a trace, he insists.
When a body is discovered in the opulent parlors lining Lyon’s back streets, Margaret and Locard employ nascent forensic methodology, striving to demonstrate the veracity and effectiveness of his Principle to skeptical judges and juries.
Can Locard and Margaret catch a killer by deciphering the vestiges of evidence left behind, or will this clever murderer slip through their fingers?
Based on true events and characters, The Exchange Principle is a story of unexpected connections and lasting impact in which the events of 1912 Lyon are told years later in post-war Florence, Italy. A final diary entry and an unexpected meeting reveal the imprints that Margaret Harkness herself will leave behind, a testament to the enduring power of human connection.
“A tale of science, suspense, and the indelible marks we leave on each other.”
– Derek McFadden, author of What Death Taught Terrence
"A top of the table forensic mystery with a real life forensic detective!"
– Advance reader review
Margaret Harkness (1854–1923) was a trained nurse, journalist, and writer (as John Law) of several notable books, and was an independent woman who passionately advocated for the disadvantaged. “In her works of social investigation, Harkness uses a tone of social realism or naturalism, making her different from her male contemporaries.” (Deborah Nord, Walking the Victorian Women, Representation, and the City. Cornell UP)
Enjoy more stories featuring this remarkable woman interwoven with real-life events by Bradley Harper.
A Knife in the Fog (novel)
London, 1888. Professor Joseph Bell and a young Arthur Conan Doyle join the hunt for the gruesome murderer soon to be known as “Jack the Ripper.” Margaret Harkness, local to the East End streets of Whitechapel, might just prove to be an indispensable ally.
Queen’s Gambit (novel)
London, 1897. Margaret Harkness accepts a plea for help when her old friend and comrade, Professor Joseph Bell invites her to join him on a secretive mission. But she soon finds herself in an assassin’s crosshairs bent on two both her and Queen Victoria.
The Exchange Principle (short story)
Lyon, 1912. Margaret Harkness steps into the smoky, intrigue-laden backstreets of Lyon, France and witnesses the birth of forensic science when Edmond Locard, a man inspired by Sherlock Holmes, struggles to prove his “Exchange Principle.” Does every contact leave a trace? Or will a clever killer slip through their fingers?
48 pages, Kindle Edition
Published April 7, 2025
1 person is currently reading
About the author
Bradley Harper
26 books106 followersBradley Harper is a retired US Army Colonel and pathologist with extensive experience in autopsies and forensic investigation. A lifelong fan of Sherlock Holmes, upon retirement from the army Harper received his associate degree from Full Sail University and master’s from Napier University in Edinburgh, Scotland, both in creative writing.
His debut novel, A KNIFE IN THE FOG, was published in October 2018 It was a finalist for a 2019 Edgar Award by the Mystery Writers of America for Best First Novel by an American Author and is a Recommended Read by the Arthur Conan Doyle Estate. It went on to win Killer Nashville’s 2019 Silver Falchion as Best Mystery. The audiobook, narrated by former Royal Shakespearean actor Matthew Lloyd Davies, won Audiofile Magazine’s 2019 Earphone Award for Best Mystery and Suspense. The book is also available in Japan via Hayakawa Publishing.
Harper’s second novel, QUEEN’S GAMBIT, won Killer Nashville’s 2020 Silver Falchion Award twice, once for Best Suspense, and again as Book of the Year.
A short animated film, DARK TRYST, based on Harper’s short story and comic book of the same name, has won numerous awards at film festivals around the world, including Best Super Short Film at the London Movie Awards, the New York Movie Awards, and the Paris Film Awards, and Best Horror at the Tokyo Short Film Festival.
Harper’s most recent works have both been collaborations. He recently released REFLECTIONS IN A DRAGON’S EYE, a police procedural thriller he co-wrote with debut novelist Lydia Galehouse, and MY TIME WITH GENERAL COLIN POWELL, co-written with Leslie Lautenslager, who worked with GEN. Powell for over 25 years.
His debut novel, A KNIFE IN THE FOG, was published in October 2018 It was a finalist for a 2019 Edgar Award by the Mystery Writers of America for Best First Novel by an American Author and is a Recommended Read by the Arthur Conan Doyle Estate. It went on to win Killer Nashville’s 2019 Silver Falchion as Best Mystery. The audiobook, narrated by former Royal Shakespearean actor Matthew Lloyd Davies, won Audiofile Magazine’s 2019 Earphone Award for Best Mystery and Suspense. The book is also available in Japan via Hayakawa Publishing.
Harper’s second novel, QUEEN’S GAMBIT, won Killer Nashville’s 2020 Silver Falchion Award twice, once for Best Suspense, and again as Book of the Year.
A short animated film, DARK TRYST, based on Harper’s short story and comic book of the same name, has won numerous awards at film festivals around the world, including Best Super Short Film at the London Movie Awards, the New York Movie Awards, and the Paris Film Awards, and Best Horror at the Tokyo Short Film Festival.
Harper’s most recent works have both been collaborations. He recently released REFLECTIONS IN A DRAGON’S EYE, a police procedural thriller he co-wrote with debut novelist Lydia Galehouse, and MY TIME WITH GENERAL COLIN POWELL, co-written with Leslie Lautenslager, who worked with GEN. Powell for over 25 years.
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Displaying 1 of 1 review
April 14, 2025
I really enjoy this author! His A knife in the Fog was a brilliant Sherlock Holmes pastiche that mashed with Jack the Ripper. Both elements worked super well together.
This short story features one of the leads from that, the real-life Margaret Harkness. And Dr. Harper this time mashes a real-life first-ever forensic case in France with a very efffective narrative device that loads on the feels. Just as as he did in his debut novel.
It's not long, but what's on the page will surely resonate and you'll get the title's layered meaning. The last page is ultimately the pot of gold at the end of this rainbow :).
Highly recommended!
This short story features one of the leads from that, the real-life Margaret Harkness. And Dr. Harper this time mashes a real-life first-ever forensic case in France with a very efffective narrative device that loads on the feels. Just as as he did in his debut novel.
It's not long, but what's on the page will surely resonate and you'll get the title's layered meaning. The last page is ultimately the pot of gold at the end of this rainbow :).
Highly recommended!
Displaying 1 of 1 review