Agatha Christie’s mystery novels are famous for their surprising twists, but even Christie’s plots are no match for math. In honor of Christie’s 125th birthday, a team of mathematicians in the U.K. have developed a formula that can easily calculate the killer in Christie classics like Murder on the Orient Express and Death on the Nile. The research analyzed 27 of the 83 novels published during her lifetime; the resulting formula takes factors like the killer’s gender, method, relationship to the victim, and mode of transport into account. Apparently Christie used different language depending on the gender of the killer: She casts female culprits in a negative light but writes about male culprits in a neutral or positive way. Sadly for you budding detective types, the formula is so dizzingly complicated that it’s probably safest to stick with Miss Marple or Hercule Poirot when crime-solving.