After a speeding fine issued by Sergeant Goodfellow, Bunty gets off as community service to give a talk at Langley Hall, a reformatory ('Borstal') for girls aged 16 to 23. Bunty's compact is stolen, and found in the possession of one of rebellious inmate Brenda, who is placed in solitary confinement. Next day the governor of the Borstal is found murdered, Brenda is on the run after hiding in Bunty's car. Father Brown and Bunty return to the Borstal to help Sergeant Goodfellow's investigation, as inspector Mallory is on annual leave. They have to unravel the lies and ill feeling between model inmate Kate (who has a secret adult ex-con boyfriend) and Brenda and tensions among the uniformed staff. The governor's liberal-leaning deputy Emily Harris takes charge over long-serving Helen Delaney, a hardliner like the late governor. Father Brown uncovers exploitation of recently released girls including missing Brenda and the newly released Kate.
—KGF Vissers