Secret of the River by Fred M. White

It was fairly early on the Wednesday morning when Blissett returned by car to his house. He had a good deal to say to Nevil, when the latter put in an appearance and most of it was vital to the success of the coming operations.

"First of all," he said. "Let me tell you about that powder. There was only a pinch of it, but quite sufficient for our purpose. It turns out to be a sort of offspring of heroin, only much more effective and dangerous. There was not enough to the powder to try experiments, but my man seems to think that it is practically a new drug of an extremely potent nature. Much stronger than cocaine, for instance."