“Oh, but, Quentin—­Mr. Locke—­I’m—­I’m so sorry.  Surely he could not have meant it.”

At the head of the stairs Locke tried to smile.

“Don’t worry,” he said, repressing his feelings.  “It will make no difference between us.  Good night.”

They parted, Eva closing her door for a sleepless night, Locke to work far into the night in his laboratory until sheer exhaustion overcame his feelings.

Meanwhile, in the dining-room, the two men kept terrible vigil, hour after hour, oblivious of time, in wild and wanton laughter—­maniacal abandon.

A terrible blow had been struck and Reason was tottering on her throne.

Two men had been stricken by an unknown hand—­stark, stark mad.

CHAPTER V

“Father—­please—­open the door!”

It was early the following morning that the butler with frightened face had called Eva Brent to tell her that her father and Flint had been locked in the dining-room all night and were still laughing madly.

Eva had hurried down-stairs, encountering Zita as she ran.  It was true.  She could hear the voices inside.  Nor could she get any answer from the two men.

“Oh—­Zita—­please—­can’t something be done?” Eva implored.

With a hasty word Zita hurried away just as Herbert Balcom himself entered the house from the street.

In utter surprise Balcom nodded at Zita as she poured forth the story of what had been discovered in the morning, then pushed past her in high excitement.

“What’s wrong?” he asked as he came upon the butler and Eva still knocking excitedly at the dining-room door.

Eva was almost in a panic as she answered, “Father and Mr. Flint have been in there laughing ever since last night.”

Balcom tried to comfort her.  But somehow his sympathy sent a cold shudder through the poor girl.

Meanwhile Zita had encountered Locke hurrying down at the sound of the commotion.  To him she told the story, again hurt that his interest was solely for Eva, not in herself.

Locke paused long enough to seize an umbrella from the rack, rip the cover off, and break out a rib, to which he tied a piece of string while he hurried to the group at the door.

“Break down the door and call the police,” ordered Balcom.

The butler reached for a chair and was about to swing it over his head to break down the door.

“Stop!” interrupted Locke.

The young scientist knelt down, inserted the umbrella steel through the keyhole, and bent it by the string as he fished about with it on the other side to find the bolt.  Meanwhile the butler telephoned frantically for the police.

It was at this height of excitement that Paul Balcom entered.  A moment’s talk with Zita, and he, too, joined the group.

Sympathetically he spoke to Eva, but Eva scarcely responded in the fashion of a girl to the man whom she was going to marry.  Her attention was riveted on Locke, who was kneeling before the door.  Paul saw it and an ominous scowl crossed his face.