Choirmaster Gareth Malone is back. He thinks the Military Wives are the perfect choice to launch the nation's centenary commemorations of the outbreak of World War I, and he pulls together a new Military Wives super-choir to stage a very special prom in association with the National Theatre's War Horse team. It is three years since Gareth formed the first Military Wives choir, and since then the organisation has mushroomed with over 80 choirs and 2,000 members around the globe. In this episode, Gareth sets out to audition as many of them as possible for his 100-strong choir. The wives usually sing pop songs, but Gareth has a repertoire of taxing classical pieces that were popular at the time of the First World War in mind, including Gustav Holst's fiendish Ave Maria set in eight-part harmony and a moving setting of Tennyson's poem Home They Brought Her Warrior Dead, so he needs to recruit the very best technical singers for what will be their toughest ever musical challenge. As the gruelling rehearsals get under way, Gareth discovers that the wives' dignity in the face of the constant threat of the death of their loved ones is as strong as ever, and the wives discover powerful parallels with their counterparts 100 years before them. The first episode culminates in an emotional performance at RAF Brize Norton for some of Britain's last deployment of troops to return from Afghanistan.

In this episode, Gareth works the wives harder than ever as they prepare to share the stage of the Royal Albert Hall with some of the world's top professional musicians on the 3rd August - the eve of the day Britain entered World War I. The wives meet the National Theatre's War Horse team who they will perform alongside, and the planned repertoire forces the wives to confront their own vulnerability. One of the serving wives makes the momentous decision to leave the Armed Forces. The episode culminates in Gareth and his 100-strong amateur choir giving the most professional and emotionally engaged performance at the BBC Proms.