British boyband Union J pop by the Music Mansion with a harmony challenge for the kids: will they manage to be beautifully in tune or an awful racket? The mums face rough tides when pulled behind a speedboat on a giant inflatable - who will manage to stay afloat the longest? With only three Sing-Off's left, the competition is hotting up - can anyone win a second Sing-Off to take the lead?

In the most difficult challenge yet, emotions are running high as the kids must compete in front of music producer, DJ and rapper, Ironik. Something's a bit fishy as the mums become mermaids for the day. Who will win the penultimate end-of-show Sing-Off?

The young singers try to master the art of performing while uncomfortable and get performance tips from former JLS singer Aston Merrygold. Find out who flies into the last Sing-Off, while the mums must face their own fears in the terrifying Leap of Faith. And who will win the fast-track pass into the Grand Final?