Running Man — Season 1, Episode 501

This week, guests Ha Yeon Ju, Kwak Si Yang, Park Hyo Ju, and Lee Yi Kyung join the show with their extraordinary detective acting skills. The race tests their intelligence and reasoning in an all-out quiz that secretly holds three illegal participants who know all the answers. The top five ranking members will win prizes only if they manage to keep two of the illegals out of the leader's board.