Sherlock works on a case involving missing women who recently arrived in London. It turns out that a taxi driver was abducting women and having them choose a poisonous pill to determine whether they lived or die. Eager for more excitement, the cabbie convinces Sherlock to play. Sherlock works through the process of trying to determine, by backward induction, which pill would be deadly.
He never finds out if he was right.
This clip was recommended by Christine Cai.