Dancing on the Edge, Series Finale, BBC Two

Stephen Poliakoff's slow-burning drama had turned into a propulsive whodunnit by this final episode, hurtling towards a resolution with panache and surprise. The five-part mini-series about a black jazz band in early 1930s high society has had the feel of an exploratory score at times. With syncopated beats and riffs decorating its unfolding narrative, the occasional scene and detail has seemed superfluous. But Poliakoff has had his reasons.

This episode juggled the escape of innocent band leader and murder suspect, Louis (Chiwetel Ejiofor), to safety from the police, alongside the search for the real killer. As Stanley (Matthew Goode), ever the dashing hero, helped Louis to hide, suspicion gathered around other characters. Masterson (John Goodman, pictured below), the wealthy American, looked increasingly shifty, buying up Stanley's music magazine with Lavinia (Jacqueline Bisset), the part-time recluse, and lavishing positions and gifts on everyone. He had already been implicated in the beating-up of a young girl. But was it him? Sarah (Janet Montgomery), the photographer, suggested he was protecting Julian. But why? It was Lavinia who came up with an answer: Masterson had homoerotic feelings for his young employee. More scandal!

The characters finally revealed their depths and their flaws. Sarah, Louis's loyal lover, gave the police a lead to help find him, while Pamela, the It girl, demonstrated surprising concern and ingenuity as a member of the fugitive party. Prejudices surfaced with alarming speed, with the apparently open-minded Lavinia deciding that tragedy was "the likely outcome" of society accepting "a negro band".

Julian (Tom Hughes) became even more - and quite brilliantly - strange. Rather than mourning Jessie, he thought about shoes: he must get new ones so that people would think he was important. There were telling clues (on more familiar Poliakoff territory) as to why he might be unhinged: he grew up with an anti-Semitic, uncaring mother. When Julian found a gun in his house, it was a clear sign that he was the killer. To unsettle Masterson, Julian took him out for bangers and mash, and shot himself. Hughes's performance was spectacular, revealing glints of turmoil behind a boyish exterior - he's a talent to watch. As for Louis, he and the band eventually caught a train to Dover, and soon Louis was looking as composed as ever, drinking in Marseille on the way to the US.

The final episode boasted cinematic photography and plenty of swishing gowns and three-piece suits (essential wear even if you're going to be spending the day in a damp basement with a runaway), soundtracked by the warming songs of the jazz band alternating with a barrage of strings for the tense moments. In Dancing on the Edge, Poliakoff has constructed a believable world, spanning turbulent class divides, and has shown how breaking convention (and the march of progress) come at the risk of losing the safety and comfort of the old ways. With so many ideas here, surely no-one could now accuse this writer of being slow to tell a story.

• The final episode of Dancing on the Edge is repeated at 22.30 on Sunday on BBC Two