The afternoon of the 9th of September was exactly like any other afternoon. None of those who were to be concerned in the events of that day could lay claim to having had a premonition of disaster. (With the exception, that is, of Mrs Packer of 47, Wilbraham Crescent, who specialized in premonitions, and who always described at great length afterwards the peculiar forebodings and tremors that had beset her. But Mrs Packer at No. 47, was so far away from No. 19, and so little concerned with the happenings there, that it seemed unnecessary for her to have had a premonition at all.)

...

Why exactly did Sheila Webb walk into 19 Wilbraham Crescent, only to discover the murdered corpse of a middle-aged man？

She didn't know the blind owner of the house, Mrs Pebmarsh. Mrs Pebmarsh denies all knowledge of ringing Sheila's secretarial agency and asking for her by name - yet someone did. And neither seems to know the murdered man.

In a case where no-one appears to know anything, the clock is ticking for Hercule Poirot - all except the clocks in the room where the murdered man was found. For all but one of those were frozen at 4.13...