The next 12 contestants including “Sherlock” the pharmacist, a nanny who feels underestimated, and student Rosie face a fresh set of challenges based on the games Mensa use to measure IQ. The tasks include code breaking, lexical perplexity, and a particularly complex cipher involving a landline phone — something the youngest contestant, Rosie, struggles with for reasons beyond the difficulty of the puzzle itself. By the end of the episode, only three contestants will earn a coveted place in the Oxford finals.