There were not twenty yards between the three of them.
What Riach saw in front was a short stout man proceeding cheerfully down the street. He delayed in a doorway to light a cigar, and the stranger stopped as if turned to stone.
Andrew stopped too.
They were like the wheels of a watch. The first wheel moved on, and set the others going again.
For a hundred yards or more they walked in procession in a westerly direction without meeting a human being. At last the first of the trio half turned on his heel and leant over the Embankment.
Riach drew back into the shade, just before the stranger took a lightning glance behind him.
The young man saw his face now. It was never fuller of noble purpose; yet why did Andrew cry out?
The next moment the stranger had darted forward, slipped his arms round the little man's legs, and toppled him into the river.
There was a splash but no shriek.
Andrew bounded forward, but the stranger held him by one hand. His clear blue eyes looked down a little wistfully upon the young Scotchman, who never felt the fascination of a master-mind more than at that moment. As if feeling his power, the elder man relaxed his hold and pointed to the spot where his victim had disappeared.