Hmm...Conan Doyle and Ellis Peters Combined

An Indian woman killed her lover by putting poison in his food.

The poison was Monk's Hood, a variety known as aconitum ferox. It was used as a plot device in the Ellis Peters mystery Monk's Hood.

The poison was added to a curry (Imagine that!), just as opium was added to curry in the Sherlock Holmes story "Silver Blaze."

"There are no new crimes, Watson," Sherlock Holmes used to lament, before reaching for the cocaine bottle.