e next instant the laboratory was re-echoing with the sound of heavy
blows upon the door.

"Open up!" roared a muffled voice. "It's the law!"

"The police!" Mark's face went pale.

Professor Duchard darted to the bench which lined one wall. Seized a
strange-looking helmet which stood there. Rushed with it to Mark.

"The insulator-helmet!" he explained hastily, his blue eyes feverish
with excitement. "Strap it on! Quickly!"

"Open up!" the alien voice roared again. "We want in!"

And then the angry accents of Adrian Vance:

"Break it down, officer! Don't let them get away!"

Mark hauled the frame on which the painting was stretched to a position
in front of the mirror. Whirled back. Gripped his companion's hand.

"Will it work, professor? Will the mirror take me back through time?"

"That I cannot tell you, my boy. But it should. You know the formula I
worked out. You understand the process by which it was constructed." A
second's pause. "Actually, I believe it should work far better than the
previous time mirror. The one Vance gave Elaine was very old, very
crude. This one is the product of modern science, modern workmanship. It
creates a tremendously larger rift in the space-time continuum--"

A shot rang out.

At the other end of the laboratory, the outside door burst open, lock
shattered. Uniformed police rushed in, Adrian Vance at their head.

"Mark! Quickly! I shall hold them!"

With a savage jerk, Elaine's fiance ripped aside the cloth that veiled
the new time mirror. The reflection of Jerbette's painting sprang across
its silver surface.

Mark's jaw went hard with tension. He glued his eyes to the figure of
Jacques Rombeau, Elaine Duchard's lover.

Behind him, Adrian Vance charged down the laboratory, struggling to
shake off the frail, tenacious figure of Professor Duchard. He brought
up his heavy Magnum.

But Mark paid him no heed. Already his brain was spinning, his senses
reeling. Yet still he concentrated on the lithe, tense figure of Jacques
Rombeau holding the fuming Baron Morriere at bay. And through his mind
the words kept ringing:

"I shall take over the brain of Jacques Rombeau! I shall save Elaine
from her fate!

"_I shall change history!_"

* * * * *

"You dog!" said Baron Morriere in a voice that trembled with passion.
"I'll see you drawn and quartered for this! You'll swing from the
highest gibbet in all France--"

"Save your breath!" snapped