“Then it shall be on your own head,” said Shelley. “I will tell you what I think has happened. You know my weakness for arguing the whole thing out like this, and, anyhow, I want you to have all the facts before you. You don’t know what I’ve been doing in the time while you were dashing about the respectable suburbs.”

“Carry on, sir,” said Cunningham, and Shelley willingly complied.

“I think that the will was a forgery. Moss was in a desperate position—for a reason which I will tell you presently and which I have only discovered quite recently—and he saw that the only way of putting things right was to get old Professor Arnell’s money left to him. But he scarcely knew Professor Arnell—he had merely heard him referred to as his rich uncle. How was he to ensure it?”

“How?” murmured Cunningham.

“He could forge a will. But a will needed to have two witnesses. Then there came the chance of Dr. Wilkinson’s death at the British Museum. Moss had seen Wilkinson as one of Arnell’s friends, and there was one witness ready made.”

“It doesn’t matter, then,” said Cunningham, “if a witness to a will dies before the testator.”

“Not a bit,” said Shelley. “If that made a will invalid half the wills in the country would be wrong.”

“I see.”

“Well,” said Shelley, “that disposes of one witness. The other witness—Crocker—very nearly muddled the whole affair for Moss. I looked through the files of The Times today, and I found that Crocker’s death was wrongly reported a few weeks ago. There was an error. Another man of the same name, also living in Oxford, had died, and it was reported as being the man whose murder we so nearly witnessed.”

“I suppose Moss found out his mistake only just in time?” Cunningham suggested.

“Yes. So Crocker had to die. But Moss had already tried to inveigle Miss Arnell’s young man in the case, and he saw in Crocker’s death the ideal opportunity of killing two birds with one stone. So he wrote that note, bringing young Baker up to town, and made sure that he would be in the vicinity of the murder. I have no doubt that he inveigled his victim to the neighbourhood of the British Museum by some similar means. It all sounds very complicated when I describe it to you like this, but it’s quite simple really.”

“And why make the will to benefit Miss Arnell and himself after her death?” asked Cunningham.

“It does seem rather curious, I must admit,” said Shelley. “Still, the main point would be to distract the immediate suspicions as to himself, which would naturally arise if the Professor had left the money to an almost unknown cousin, and had disinherited his only daughter.”

“H’m.” Cunningham did not seem to be altogether convinced by this explanation.