Pitch Battle adds its special twist to the iconic Doctor Who theme tune.
This episode's six groups include an a cappella group from King's College London called All the King's Men, Polish jazz group Alle Choir, the London International Gospel Choir, female vocal soul group Songbird Sessions, Welsh choir Sgarmes, and the newly formed 4 Tune Tellers and Kimmy.
To progress, the groups must impress the panel of musical judges - the nation's favourite choirmaster Gareth Malone, former choirgirl-turned-international recording artist Kelis, and superstar guest judge singer-songwriter Bebe Rexha.
The programme opens with an epic musical mash-up, arranged by the series musical director Deke Sharon, who is the musical director on the Pitch Perfect movies.
Groups then go head to head in a series of knockout choral challenges. First they each perform their showstopper before battling it out with their opponent in a themed riff-off. The judges then decide which group goes through to the solo battles later on.
At the end of the programme only two groups will remain, where they must face the ultimate sing-off - the final battle. Here they share the same song, before superstar guest judge Bebe Rexha joins in with the group the judges have chosen to go through to the final.
Bebe Rexha will return in the grand final to sing with the show's winning group, who will be one step closer to the £50,000 cash prize.
All the acts open the show with a 'Party' themed number.
All the showstopper performances from tonight's show.
This show was recorded before the Grenfell Tower tragedy and the theme of one of the Riff Offs was "Fire". Due to some of the lyrics, we feel it would be insensitive to show it in full. Both of the lovely choirs involved fully support this decision.
Rob, Gemma and Kedma their choirs in the Solo Battle.
‘Take Me Home’ featuring Superstar Guest Judge Bebe Rexha.