The cab took her into a street lined with tall edifices and left her at the number she had given the driver.

The building seemed to be one let out in flats and tenements; she mounted stair after stair, and only at the very top did she see the Professor's name painted on a door.

Here she rapped several times without any attention being paid to her summons, but at last the door was opened partially by a man whom she took, quite accurately, to be the Professor himself.

His head was white; and his face deeply wrinkled.

He glared at her through his glasses, and said sharply, "Young lady, you have made a mistake; these are the rooms of Professor Carl Seigfried." "It is Professor Carl Seigfried that I wish to see," replied the girl hurriedly, as the old man was preparing to shut the door.
"What do you want with him ?" "I want some information from him about explosives.