"But we haven't all the radioactive matter that Odin will need," I protested.
"We have most of it. If you perish here, we'll never get even this much back to him. Quick, up the stair to the disk!"
He grabbed the crucible's handle. Reluctantly I took the other handle and started with him toward the stair. As we hastened with our heavy load between the roaring geysers of atomic fire, I looked back. The one of the flame-children that had touched me experimentally was now joining several other dazzling creatures like itself, and drifting after us.
Hastily we started up the stair. With some relief, I saw that the flame-children did not follow us, but drifted on and started circling and flitting around another of the fire fountains. Apparently the dim intelligence of the creatures, if indeed they possessed any, had lost interest in us.
Panting and exhausted, we reached the landing and set the crucible down on the floating disk. Thor hastily adjusted the controls to make up for the increased weight on it. As he crouched down, preparatory to starting up the shaft, I noticed something.
"Thor, what is that door up there, high in the roof?" He turned his gaze to follow my pointing finger. The door looked like a massive sliding sheet of dull metal, set in the roof of the underworld some distance from us. There was a shielded mechanism of some kind set in the rock by the door, obviously controlling it.
"That is the forbidden research upon which Loki was engaged, and which caused us to banish him from Asgard," Thor explained. "Above that door is a tunnel connected with the sea of the upper world. If the door were opened, sea water would rush down into this underworld."
"Good lord!" I cried in horror. "If sea water ever poured down into this world of fire, there'd be an explosion that would shake the planet!"
"Aye, and Odin saw that danger," Thor said. "Loki planned to admit only enough sea water to produce the titanic power of which he had need in his experiments. But Odin pointed out that if anything went wrong — if this door were completely opened and the sea rushed down unchecked into Muspelheim — there would be such an explosion as would rend the whole land above. It was the reason for Loki's banishment."
As Thor spoke, he was moving the control lever. The floating disk began to rise in the vertical shaft, out of the fiery underworld. With all the tiny valve-doors closed, it rose quickly under the pressure of the powerful radiation. We shot up the dark shaft at a speed that almost equaled that of our descent.