They were not seen, were sailing in giant steps up
another stair, hopes rising high. The last stair--the roof-opening
above; and then from beneath a great croaking cry swelled instantly
into chorus of a alarmed shouts.

"They've found the door--the guard!" panted Hackett.

They were bursting out onto the roof. Frog-guards were on it who came
in a hopping rush toward them, force-pistols raised. But a giant leap
took Hackett among them, to amaze them for a moment with great
flailing blows. Sarja had leaped for the nearest flying-boat resting
on the roof, and was calling in a frantic voice to Norman and Hackett.
Norman was turning toward Hackett, the center of a wild combat, but
the latter emerged from it for a brief second to motion him
frantically back.

"No use, Norman--get away--get away!" he cried hoarsely, frenziedly.

"Hackett--for God's sake--!" Norman half-leaped to the other, but an
arm caught him, pulled him desperately onto the boat's surface. It was
Sarja, the long craft flying over the roof beneath his control.

"They come!" he panted. "Too late now--" Frog-men were pouring up onto
the roof from below. Sarja sent the craft rocketing upward, as Hackett
gestured them away for a last frantic time before going down beneath
the frog-men's onslaught.

* * * * *

The roof and the combat on it dropped back and beneath them like a
stone as their craft ripped across the silvery dusk over the mighty
frog-city. They were shooting toward the city's center, toward the
green pool that was the entrance to the water-tunnel, while behind and
beneath an increasing clamor of alarm spread swiftly. Norman raged
futilely.

"Hackett--Hackett! We can't leave him--"

"Too late!" Sarja cried. "We cannot help him but only be captured
again. We escape now and come back--come back--"

The truth of it pierced Norman's brain even in the wild moment.
Hackett had fought and held back the frog-guards only that they might
escape. He shouted suddenly.

"Sarja--the water-tunnel!" A half-dozen boats with frog-guards on them
were rising round it in answer to the alarm!

"The force-gun!" cried the green man. "Beside you--!"

Norman whirled, glimpsed the long tube on its swivel beside him,
trained it on the boats rising ahead as they rocketed nearer. He
fumbled frantically at a catch at the gun's rear, then felt a stream
of shells flicking out of it. Two of the boats ahead vanished as the
shells release