I'm writing the climax of a story set in an expy of Victorian London (circa 1860's). The heroes are exhausted and sleep deprived, and heading into a firefight. The thought occurred that they might resort to some chemical assistance to bring their energy up. I know cocaine was available in the 19th Century, but what else might be lying around?

And what is the window for the effects to stay in their systems? And just generally, how will someone on a powerful stimulant feel? I've never used any stimulant other than caffeine and energy drinks.