The lives of four singers are far from harmonious. Danny's marriage is on the rocks, while Vince is struggling with a debilitating illness. Henry is having a mid-life crisis, and Neil is at war with his father. But when they sing together none of that matters. Because something magical happens. On a mission to compete against the best quartet singers in Britain, they turn to veteran entertainer, Ken, who inspires them to discover a curious vocal technique called 'The Fifth Voice'.