Canon Fox (Roger May) pays a visit to inform Father Brown (Mark Williams) and Mrs McCarthy (Sorcha Cusack) that the Duke of Frome, John Langton (Ray Coulthard) will be attending Christmas Mass at St Mary's. This year the Bishop wants everything done by the book and Canon Fox will be there to make sure it all goes to plan... Lady Felicia (Nancy Carroll) is delighted to welcome her cousin the Duke, his wife Diana (Zannah Hodson) and baby David to stay at Montague. Later at the Yuletide ball Inspector Mallory (Jack Deam) is informed that the infant is missing. With a ladder against the nursery window, the Inspector surmises that the baby has been kidnapped; all they can do now is wait. Can Father Brown find the child in time for Christmas?