France, 1944. Rosemary Brown is sent to the Marneville Internment Camp for British Women. En route, she meets cheerful Freda Thompson, man-hungry Bridie Johnson, haughty Miss Manningford, and her dowdy companion Miss Meredith.

At the camp, the women are taken to Sergeant Hentzner, the German officer who allocates accommodation. Freda and Rosemary share, as do the Misses Manningford and Meredith, while Bridie uses feminine wiles to get a single room.

The stern Frau Holweg introduces them to group leader Teresa King. They meet their fellow inmates, and Freda hits it off with no-nonsense Scotswoman Maud Wright.

Freda and Rosemary's bath is a public affair, with women crowding round the tub. Monsieur Boper, the owner of the spa that became the Marneville camp, wanders in and out.

A radio turns up in the kitchen, addressed "to the women of Marneville". The Germans confiscate it, which leads to speculation as to who informed them.

Nellie tells Freda and Maud that Rosemary was arrested while dressed as a nun. Rosemary confirms that it's true - but she's a real nun. Maud sees Bridie and Sergeant Hentzner having a surreptitious conversation.

At 10pm, Bridie feigns a headache and asks Teresa for the kitchen keys. Hentzner grooms himself, but has to join the other Germans when an air raid starts. Misses Manningford and Meredith listen to the RAF plane above and shine a light from their window.

Pilot Officer Jimmy Moore and Sergeant Alec Harvey land in the grounds and investigate the building. Jimmy ends up in Rosemary's room, Alec with Misses Manningford and Meredith. Freda and Maud discover what's going on and hide them.

The next day, the women plan the men's escape - on Saturday, under cover of a forthcoming concert. Monsieur Boper admits to supplying the radio and suggests his secret wine cellar as a hiding place, and gives Rosemary the key. Searching for the back door key in Teresa's room, they find her Nazi Party membership card.

Everyone in the camp is summoned to the lobby. Bridie refuses to go, as she's sprained her ankle - Hentzner decides not to force her. She's actually sheltering another airman, Dave Kennedy.

Frau Hollweg announces that a British bomber crew is hiding in the camp. Whispered rumours start to ripple outwards. Freda passes on the news that Teresa is a Nazi spy, and the whispers stop before they reach her.

Rosemary shows the men to the wine cellar. Jimmy asks her to meet him later that evening. Alec is convinced she's Mary Maugham, a singer caught up in a marital scandal when her lover tried to poison his wife. He recalls her signature song.

Jimmy sees Rosemary, and incorporates the song lyric into a sentence. Her reaction confirms her as Mary Maugham. She reveals that she went to the convent to escape the scandal, but she never took her vows. They kiss.

Hentzner goes to Bridie's room and sees Dave. A fight breaks out. Jimmy and Rosemary investigate and find Hentzner strangled.

The women plan a one-minute blackout during the concert. The Germans are suspicious as Hentzner has disappeared, and the Gestapo has been summoned. Freda suggests that Bridie does a striptease to distract them at the end. But Bridie won't co-operate, as she doesn't want Dave to escape.

The Misses Manningford and Meredith are shipped off to a German camp for signalling to British airmen. The women spontaneously sing their support as they leave.

The concert begins. Jimmy proposes to Rosemary, but she says no. Freda persuades Dave to see Bridie again, but he's furious at her liaison with Hentzner. She storms off before Freda has a chance to explain. Jimmy offers to help him write a note, which is passed on to Bridie in her room.

But Bridie has decided to confront Teresa and reveal that the others know what she really is. A fight breaks out, which Bridie loses. Teresa goes to tell Frau Holweg about the plan, but Maud knocks her unconscious. Rosemary offers to go on stage in Bridie's place.

The blackout occurs on schedule, and the men escape. An angry mob descends on Teresa. The women sing "There'll Always Be An England", with the Germans powerless to stop them.