Adelaide Bartlett was a young French woman living in England, who got into a love triangle with her husband and another man. When her husband turned up dead one day though, the whole arrangement fell apart and she suddenly became a murder suspect.
Sources and Resources:
“The impossible case of the Pimlico poisoning,” The CutPrice Guignol, https://thethreepennyguignol.com/2024/04/17/the-impossible-case-of-the-pimlico-poisoning/
Farrell, M. “Adelaide Bartlett and the Pimlico Mystery,” https://pmc.ncbi.nlm.nih.gov/articles/PMC2542684/pdf/bmj00471-0054.pdf
Wikipedia