Three young VAD's (Voluntary Aid Detachments) go to Hospital 25A near the front in Boulogne. However, it isn't what the trio expect and lots of troubled events occur along the way.

Paranoia is rife as the hospital anticipates the court martial of a patient. Thomas's pioneering system brings him into conflict with a senior officer.

A band of patients known as the Lucky 13 lift spirits in the hospital but one holds a secret which could threaten their safety. The return of a patient spells trouble for Margaret.

A hostile patient forms a connection with Grace as she recalls her time in India, and Joan risks everything as she awaits a response from her fiancé.

Grace realises that something is up with Kitty as she keeps her distance. A Major wakes up from the verge of death, still badly wounded he also has to find out that his troops have been decimated. The hospital prepares itself for a convoy of new patients.

The hospital is thrown into disarray as Joan faces a charge of aiding the enemy.