Nor were his fears unfounded.  He had barely passed the fountain where, half an hour before, he had been set free, when an emissary came out from behind a neighboring tree and took up his trail.

De Luxe Dora also had waited only long enough to see Eva and Locke enter Brent Rock, when she turned her runabout around and drove rapidly back to Professor Hadwell’s.  She arrived there just in time to meet an automobile coming from the opposite direction and containing three emissaries of the Automaton.

In answer to an inquiry, Dora pointed out the chemist’s house to them.  They piled out, and their leader knocked at the door, while Dora drove off.

The chemist answered, and the leader produced a vial, glibly lying as he handed it over.

“The Williams Drug Company sent me to have this stuff analyzed,” said the leader.  “I’ll wait.”

As the professor admitted him he did not see the other two men pressed close to the wall on either side of the door.  The moment the professor’s back was turned they slinked after their leader into the house.  In a dark corner of the hallway they crouched as their leader went into the laboratory with the chemist.

The professor sniffed at the vial, which contained nothing but pure water, and in surprise turned to the emissary for an explanation.  But it was too late.  The emissary dealt him a blow with a blunt instrument that stunned him and, as he reeled back and grasped at a table, the other thugs rushed from the hall and rained blow after blow on his venerable head and beat him to the floor.  A convulsive shudder—­a long-drawn-out sigh—­and he lay still.

With barely a glance at him the emissaries set to work to smash all the paraphernalia of the place, sparing nothing in order to make sure that the antidote would be destroyed.  Glass tubes, retorts, bottles, even furniture were smashed to bits in their orgy of ruin—­and there, in the midst of the debris, his life’s work finished, lay the old chemist, dead.

Tiring of their own efforts, the murderers at last desisted.  One of them went to the street door and peered out, but in a moment was back with the others.

“Quick—­that fellow Locke is coming.”

He was right.  Locke had immediately quit Brent Rock and had come directly to the chemist’s in the hope of forestalling any further attempt by Flint to inveigle Eva into dealing with him.

The door had been left ajar and, although he thought it strange, Locke was without suspicion and entered the hallway.  He called to his old friend, but the dead lips could not answer and the emissaries would not.

Greatly alarmed now, Locke strode to the laboratory.  For a moment he stood as though petrified as the horrid scene burst upon his vision.  He ran to the chemist and knelt beside his battered body.

With a rush the emissaries darted from their hiding-place and were upon him.