Well, said Mary, "I expect he will be back before dinner." But night fell, and Poirot had not returned. 
Mary waited for Poirot until eleven in the evening but he still hadn't returned. 
mnli hypothesis: Mary waited for Poirot until eleven in the evening but he still hadn't returned.  premise: Well, said Mary, "I expect he will be back before dinner." But night fell, and Poirot had not returned. 