He started round and looked.

Yes; as he thought in all the laboratory there was only one bell that could ring, none other had its batteries charged, and that bell was attached to the aerophone whereof the twin stood upon the altar in the Dead Church.

The instrument was one of the pair with which he had carried out his experiments of the last two months.
His heart stood still.

"Great God! What could have caused that bell to ring ?" It could not ring; it was a physical impossibility unless somebody were handling the sister instrument, and at four o'clock in the morning, who could be there, and except one, who would know its working?
With a bound he was by the aerophone and had given the answering signal.
Then instantly, as though she were standing at his side in the room, for this machine does not blur the voice or heighten its tone, he heard Stella speaking.
"Is it you who answer me ?" she asked.
"Yes, yes," he said, "but where are you at this hour of the night ?" "Where you left me, in the Dead Church," floated back the quick reply through the raving breadths of storm.

"Listen: After you went my strength gave out and I suppose that I fainted; at least, a little while ago I woke up from a deep sleep to find myself lying before the alter here.