Robert Louis Stevenson 
The Strange Case of Dr Jekyll and Mr Hyde 

'He put the glass to his lips, and drank at one gulp. A cry followed; he reeled, staggered, clutched at the table and held on, staring with injected eyes, gasping with open mouth; and as I looked there came, I thought, a change – he seemed to swell – his face became suddenly black and the features seemed to melt and alter…’Troubled by the strange behaviour of his friend, Dr Jekyll, a young London lawyer decides to investigate. But the truth, as he discovers that Jekyll and the brutal Edward Hyde are one and the same is more terrible than he could possibly have anticipated…