On the morning of Christmas Eve, Father Brown deduces that someone left Baby Jacob in the Nativity Scene's manger inside the church around 7 AM since, in part, the church had been open since Midnight Mass. But since it was Christmas Eve, Midnight Mass had not been celebrated yet.
Nearly all British ducal titles are inheritable only in the male line. Given that Basil Urquhart was heir presumptive to the Duke of Frome until the recent birth of a son, they ought to have the same surname. But Urquhart says, "Two wars have left the male Langtons distinctly thin on the ground."
Set at Christmas, all the trees are in full leaf when the guests arrive at the Manor, yet the following day, all the leaves have gone in the woods leaving bare branches.
Set at Christmas spring flowering forsythia bushes are in full flower.
Set at Christmas, all the deciduous trees like Chestnuts are in full leaf.
Being a priest on Christmas Day, Canon Fox would undoubtedly have con-celebrated the Christmas morning Mass with Father Brown.