"It must be ever remembered that digitalin is a cumulative poison, and that the same dose, harmless if taken once, yet frequently repeated becomes deadly; this peculiarity is shared by all poisons affecting the heart."

He stood looking at the page.

"This peculiarity is shared by all poisons affecting the heart."

He moved his head as if in assent. Then he closed the book slowly and switched off the light.

On the August Bank Holiday, one of the most dreadful days of London's year, he set out to call on Mrs. Chepstow.

A stagnant heat pervaded London. There were but few people walking. Few vehicles drove by. Here and there small groups of persons, oddly dressed, and looking vacant in their rapture, stared, round-eyed, on the town. Londoners were in the country, staring, round-eyed, on fields and woods. The policemen looked dull and heavy, as if never again would any one be criminal, and as if they had come to know it. Bits of paper blew aimlessly about, wafted by a little, feverish breeze, which rose in spasms and died away. An old man, with a head that was strangely bald, stared out from a club window, rubbed his enquiring nose, looked back into the room behind him and then stared out again. An organ played "The Manola," resuscitated from a silence of many years.

London was at its summer saddest.

Could Mrs. Chepstow be in it? Soon Isaacson knew. In the entrance hall of the Savoy, where large and lonely porters were dozing, he learnt that she was at home. So be it. He stepped into the lift, and presently followed a servant to her door. The servant tapped. There was no answer. He tapped again more loudly, while Isaacson waited behind him.

"Come in!" called out a voice.

The servant opened the door, announcing: