Complex sentence: Refusing to play the pill game and calling off the cabbie's gun bluff (which in reality is a novelty cigarette lighter), Sherlock walks off, but he's challenged once again to choose a pill to see if he'd got it right.
Split into simpler sentences: Refusing to play the pill game and calling off the cabbie's gun bluff (which in reality is a novelty cigarette lighter), Sherlock walks off. However, he's challenged once again to choose a pill to see if he'd got it right.