Through the gloom he vaguely saw the arm of the man who stood in front of
the port raised to a level with his head, while his hand moved rapidly.

Instantly he knew what was happening. This man was signalling. Carrington
had heard of the German signalling lamp which, by means of ingeniously
arranged lenses, throws one tiny ray which can be caught and flung back by
a specially constructed mirror. That was what was happening before his
very eyes. A glow of rage sent the blood boiling through his veins, and
forgetting all about the switch he sprang forward.

As ill luck had it, there was a wooden grating in the middle of the cement
floor. In the darkness, he failed to see this, and catching his toe,
stumbled and fell with a crash on hands and knees.

He heard a terrified yelp, and the man made a dash past him for the door.

But the door was closed. Carrington had shut it behind him. Before the
fellow could get it open, Ken was on his feet again, and had flung himself
on the signaller.

With a snarl like that of a trapped cat, the man wrenched one arm free.

'Take that!' he hissed, and next instant Ken felt the sting of steel
grazing his left shoulder. The sharp pain maddened him, and his grip
tightened so fiercely that he heard the breath whistle from his opponent's
lungs.

At the same time he flung all his weight forward, and the other, thrown
off his balance, went over backwards and came with a hollow crash against
the door.