“Here, Mulligan,” ordered a sergeant, “you and Murphy take this Jap to the Emergency quick.  You, Kelly and Flannigan, get over to the box and call the police boats with drags.  Tell ’em to drag the river from Madison street in one direction and from the lake in the other.  It sounds like a dream, but this thing has got to be cleared up.  Them shots come from the river sure’s my name’s Harrigan.  We got to find how it’s done.”

A half hour later, two innocent looking police boats moved silently up the river from Madison street bridge.  They traveled abreast, keeping half the river’s width between them.  From their bows there protruded to right and left, heavy iron shafts.  From these iron shafts, at regular intervals, there hung slender but strong steel chains.  These chains reaching nearly to the bottom of the river were fitted up at the lower end with heavy pronged steel hooks.  At that same moment, two similarly equipped boats started up the river from the lake.  They were combing the river with a fine tooth comb.

* * * * *

Meanwhile the men beneath the surface of the river were not idle.  They did not realize the danger which their last act had drawn them into and therefore did not attempt to escape by running their craft out into the lake.  But they did have other matters to attend to.  One of their number was locked in the rear compartment.  His fate was unknown to them.  This much they did know, he had not unfastened the door nor answered when they called to him.

After vainly pounding and kicking the door, they lifted a heavy steel shaft and using this as a battering ram, proceeded to smash the door from its fastenings.  At first this did not avail.  But at last each succeeding blow left a slightly larger gap between the door and its steel jamb.  Then suddenly, after a violent ram, which sent echoes through the compartment, the lower catch gave way.  With a hoarse shout the Russian urged his men to redoubled effort.  Three more times they backed away to come plunging forward.  The third blow struck the door at the very spot where the fastening still hung.  And then, with a creaking groan the door gave way.

Just inside the door, Mazie stood tense, motionless, her arms outstretched in terror.  Fingers rigid, lips half-parted in a scream, she stared at the door.  In the doorway stood the Russian, a knife gleaming in his hand.  For a second his eyes searched the room.  Then they fell on the body of the Jap huddled on the floor.  Rage darkened his face as the Russian took a step forward.

At that instant there had come a dull sound of metal grating on metal.  The Russian toppled over on his side and the two girls were thrown to the floor.

The chamber had given a sudden lurch.  The next instant it rolled quite over, piling the two women and the corpse in a heap and sending the door shut with a bang.  The Russian had fallen outside.  The craft rolled over, once, twice, three times and then hung there, with the floor for its ceiling.