premise: But in her hurry to be in time for the village entertainment Mrs. Inglethorp forgot to take her medicine, and the next day she lunched away from home, so that the last ”and fatal ”dose was actually taken twenty-four hours later than had been anticipated by the murderer; and it is owing to that delay that the final proof ”the last link of the chain ”is now in my hands." Amid breathless excitement, he held out three thin strips of paper. 
hypothesis: Because Mrs. Inglethorp took her medicine later than expected, the murderer will be caught.