In Chapter 8 of The Strange Case of Dr. Jekyll and Mr. Hyde Poole goes to Mr. Utterson's home with the plea that he believes "foul play" has been committed in Dr. Jekyll's experiment cabinet. "Foul play" is an English idiom that means a murder or other foul crime has been committed (idiom: a figurative phrase that means something very different from the literal meanings of the words: "dirty laundry" is an idiom meaning family or personal secrets).
He tells Utterson that "eight days ago" Dr. Jekyll was done away with somehow and that someone else is in the Dr.'s cabinet. He and Utterson finally confess to each other that they both believe the other person to be none other than the evil Mr. Hyde. Poole believes that Hyde has murdered Jekyll. What they find when they break in the door is Mr. Hyde dead on the floor from arsenic poisoning ("kernels") and a confession letter from Dr. Jekyll.