Good memory, Jura! I'd forgotten about that story! In the Sherlock Holmes story, victims are poisoned with a powder of an African root called Radix pedis diaboli (“Devil’s-foot root” in Latin). t seems it's best known for being mentioned in that story. I assume it's real, although I haven't yet found a reference to it that isn't about Holmes. Doyle was a doctor who usually liked accurate technical details. The traditional image of a devil had cloven hooves, like a goat. So most likely that root resembles a goat's foot, hence the name.

I am not sure if this is what you are looking for.The Adventure of the Devil's Foot follows one of the 58 tales of famous detective Sherlock Holmes as written by Sir Arthur Conan Doyle. The phrase can also be used as a curse. A 'red figure' means someone dressed in red or in fairy tales often the devil was shown as a red figure with a pitchfork in hell.