ough. "I don't quite
follow," he said as he handed it back. "It hints that Grell will be
charged with the murder."

"Exactly. It is intended to convey that impression. To tell you the
truth, I have a piece of evidence of which I have not spoken to you
before. It indicates a person possibly guilty whom we must not neglect.
If she is guilty--which I half doubt--that paragraph may help us to get
at the missing evidence."

His voice sank to a whisper and he leaned forward with arms outspread
over his desk. As he spoke, Thornton's voice changed. He leapt to his
feet and brought his fist down vehemently on the desk.

"I don't believe it, man!" he cried. "I don't believe it! It's
incredible. You've made a mistake. It can't be. Why, you've believed it
was Grell yourself all along. If you've made a mistake, then why not
now?"

Foyle's chin became a trifle aggressive. Thornton's astonishment was
natural, but the superintendent did not like the appearance of lack of
confidence. His blue eyes were alight. "You can draw your own inference
from the facts, Sir Hilary," he said coldly. "I am clear in my mind. I
have done nothing, because I want to make the evidence as to motive
indisputable. Should I find I am wrong I shall, of course, write out my
resignation."

Thornton was not usually an impulsive man. He had recovered himself
immediately upon his outburst and was once more calm and self-possessed.

"Don't be offended, Foyle," he said, more mildly. "I beg your pardon. It
was just a bit startling at first. We've been associated too long for
misunderstanding. I'll back you up, and there's not going to be any talk
of resignations."

"Thank you, Sir Hilary," said the superintendent, entirely mollified.
Going to the big safe he unlocked it and took something from the shelf
which he handed to the Assistant Commissioner. The two bent over it.

It was nearly two hours before the two concluded their task. Sir
Hilary, his hands clasped behind his back, walked in deep thought back
to his own room. Heldon Foyle put on his hat and coat and ordered a
taxi.

"Brixton Prison," he said to the driver.

CHAPTER L

There are many people who pass Brixton Prison everyday who have no
conception of its whereabouts. The main entrance is tucked away a
hundred yards or so down an unobtrusive turning off Brixton Hill. Within
a little gate-house inside the barred gates a principal warder sits on
duty.

Although Foyle was tolerably well