Gareth Malone's continues his search for the nation's most entertaining amateur a cappella group - without instruments or backing tracks, they must rely solely on their voices. In this episode, Gareth brings the six surviving groups together for the first time, to contend with intensive mentoring at the state-of-the-art Performance Hub. The focus is on vocals. With the help of the best in the business, Gareth will tutor each group to improve their sound before they go head to head once more. They will compete in front of a live audience and a jury of a cappella experts - their votes decide who stays in the contest and which group will be heading home. Amid the gruelling training, two groups grapple with bringing emotion to their performances, while disaster strikes for another when an ill-judged high five takes an unexpected toll.