Alfred Hitchcock Presents:Our Cook's a Treasure (1955)

Shortly after having a quick breakfast with his wife and the new cook whom they have recently hired, Ralph Montgomery suffers a bad attack of indigestion, and continues to have trouble afterward. Later, he reads a newspaper story about a housekeeper who has poisoned several of her employers, and who is still at large. Ralph begins to suspect the worst, and he takes a cup of cocoa from the kitchen to a chemist, in order to have it analyzed.