Fourteen year old Ruth Bennett is alleged to have contracted radiation sickness after visiting the atomic power station where her father Geoffrey works and the villagers call a meeting,demanding she leave the area before she contaminates them. Next day she has vanished. Father Brown discovers a love letter from Ruth to Michael Evans,the family doctor,who has just resigned from treating her and a diary in Ruth's bedroom suggests an affair between them,which Michael denies. Valentine suspects he killed her to prevent her disclosing the relationship. Father Brown believes the doctor and reckons that Douglas,a friend of the family,knows more than he is admitting and that he can locate Ruth alive - and well.
A strange episode that has no murder, just a girl with an ailment who has disappeared- all kinds for her disappearance is proposed. I must say I found this episode quite perplexing and only till the end the truth comes out. It's well acted by all.