"It is what our mutual friend Napoleon would call a negative problem in strategy," the Assistant-Commissioner replied. "I want to ask an ethereal friend, who exists somewhere in space, to come in and be killed."

Captain Almack led the way up a flight of stairs.

"We got a request from your Commissioner; and, of course, the Lords of the Admiralty are only too pleased to put the instrument at your disposal."

"They are very charming," murmured T. B.

"They instructed me to keep a watchful eye on you. We have missed things since your last visit."

"That sounds like a jovial lie," said T. B. frankly.

In the orderly instrument room they found an operator in attendance, and T. B. lost no time.

"Call N.H.C," he said; and, whilst the instrument clicked and snapped obedient to the man's hand, T. B. opened his little exercise book and composed a message. He had finished his work long before any answer came to the call. For half-an-hour they waited whilst the instrument clicked monotonously. "Dash-dot, dot-dot-dot, dash-dot-dash-dot."

And over and over again.

"Dash-dot, dot-dot-dot, dash-dot-dash-dot."