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.

The two fell to the floor together, and rolled over, fighting like wild
cats.

Ken's adversary was smaller than he, but he seemed amazingly strong and
active. He wriggled like an eel, all the time making frantic efforts to
get his right hand free, and use his knife again.

But Ken, aware of his danger, managed to get hold of the fellow's wrist
with his own left hand, and held it in a grip which the other, struggle as
he might, could not break. At the same time, Ken was doing all he knew to
get his knee on his enemy's chest.

It was the darkness that foiled him--this and the eel-like struggles of
his adversary. At last, in desperation, he let go with his right hand, and
drove his fist at the other's head. He missed his face, but hit him
somewhere, for he heard his skull rap on the floor, while the knife flew
out of his hand, and tinkled away across the cement floor.

Ken felt a thrill of triumph as he heaved himself up, and getting his
knees on his adversary's chest, seized him with