The_Complete_Chronicles_of_Narnia_(volumes_1-7,_in_order_of_publication)

The prisoner was now so straining at his bonds that they cut into his wrists and ankles.
"Beware," he said. "Beware. One night I did break them. But the witch was there that
time. You will not have her to help you tonight. Free me now, and I am your friend. I'm
your mortal enemy else."
"Cunning, isn't he?" said Puddleglum.
"Once and for all," said the prisoner, "I adjure you to set me free. By all fears and all
loves, by the bright skies of Overland, by the great Lion, by Aslan himself, I charge you -
"
"Oh!" cried the three travellers as though they had been hurt. "It's the sign," said
Puddleglum. "It was the words of the sign," said Scrubb more cautiously. "Oh, what are
we to do?" said Jill.
It was a dreadful question. What had been the use of promising one another that they
would not on any account set the Knight free, if they were now to do so the first time he
happened to call upon a name they really cared about? On the other hand, what had been
the use of learning the signs if they weren't going to obey them? Yet could Aslan have
really meant them to unbind anyone even a lunatic - who asked it in his name? Could it
be a mere accident? Or how if the Queen of the Underworld knew all about the signs and
had made the Knight learn this name simply in order to entrap them? But then, supposing
this was the real sign? . . . They had muffed three already; they daren't muff the fourth.
"Oh, if only we knew!" said Jill.
"I think we do know," said Puddleglum.
"Do you mean you think everything will come right if we do untie him?" said Scrubb.
"I don't know about that," said Puddleglum. "You see, Aslan didn't tell Pole what would
happen. He only told her what to do. That fellow will be the death of us once he's up, I
shouldn't wonder. But that doesn't let us off following the sign."
They all stood looking at one another with bright eyes. It was a sickening moment. "All
right!" said Jill suddenly. "Let's get it over. Good-bye, everyone ...!" They all shook
hands. The Knight was screaming by now; there was foam on his cheeks.
"Come on, Scrubb," said Puddleglum. He and Scrubb drew their swords and went over to
the captive.
"In the name of Aslan," they said and began methodically cutting the cords. The instant
the prisoner was free, he crossed the room in a single bound, seized his own sword
(which had been taken from him and laid on the table), and drew it.