She went obediently up the path towards the cottage. Mortimer strolled on a little further, then threw himself down on the green turf. He closed his eyes, detached himself from conscious thought or effort, and let a series of pictures flit at will across his mind.

Johnnie! He always came back to Johnnie. Johnnie, completely innocent, utterly free from all the network of suspicion and intrigue, but nevertheless the pivot round which everything turned. He remembered the crash of Mrs Dinsmead’s cup on her saucer at breakfast that morning. What had caused her agitation? A chance reference on his part to the lad’s fondness for chemicals? At the moment he had not been conscious of Mr Dinsmead, but he saw him now clearly, as he sat, his teacup poised halfway to his lips.

That took him back to Charlotte, as he had seen her when the door opened last night. She had sat staring at him over the rim of her teacup. And swiftly on that followed another memory. Mr Dinsmead emptying teacups one after the other, and saying ‘this tea is cold’.

He remembered the steam that went up. Surely the tea had not been so very cold after all?

Something began to stir in his brain. A memory of something read not so very long ago, within a month perhaps. Some account of a whole family poisoned by a lad’s carelessness. A packet of arsenic left in the larder had all dripped through on the bread below. He had read it in the paper. Probably Mr Dinsmead had read it too.

Things began to grow clearer . . .

Half an hour later, Mortimer Cleveland rose briskly to his feet.

It was evening once more in the cottage. The eggs were poached tonight and there was a tin of brawn. Presently Mrs Dinsmead came in from the kitchen bearing the big teapot. The family took their places round the table.

‘A contrast to last night’s weather,’ said Mrs Dinsmead, glancing towards the window.

‘Yes,’ said Mr Dinsmead, ‘it’s so still tonight that you could hear a pin drop. Now then, Mother, pour out, will you?’

Mrs Dinsmead filled the cups and handed them round the table. Then, as she put the teapot down, she gave a sudden little cry and pressed her hand to her heart. Mr Dinsmead swung round his chair, following the direction of her terrified eyes. Mortimer Cleveland was standing in the doorway.

He came forward. His manner was pleasant and apologetic.

‘I’m afraid I startled you,’ he said. ‘I had to come back for something.’

‘Back for something,’ cried Mr Dinsmead. His face was purple, his veins swelling. ‘Back for what, I should like to know?’

‘Some tea,’ said Mortimer.

With a swift gesture he took something from his pocket, and, taking up one of the teacups from the table, emptied some of its contents into a little test-tube he held in his left hand.

‘What—what are you doing?’ gasped Mr Dinsmead. His face had gone chalky-white, the purple dying out as if by magic. Mrs Dinsmead gave a thin, high, frightened cry.