Gareth takes them to London for their next rehearsal and has a big surprise to drop on them: he wants them to write their own lyrics for the song they'll perform at the ceremony.
The song-writing process challenges the choir to dig deep into their experiences of injury or illness, and the stages of recovery they are in. Even Gareth struggles with his own emotions after hearing some of the stories and he wonders if he'll be able to do this mission justice.
As the choir hears the lyrics for the first time, will they like it? As he tries to help them cope with the stress of performing, it's not long before they head off to the US. Can they perform their one final duty in front of people like Prince Harry and Michelle Obama?
Gareth's Invictus Choir, BBC1, 9pm
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