(by theowinthrop on 5 December 2008)

When you see the Alec Guiness film THE DETECTIVE, the basis for that film is THE BLUE CROSS, the first story G. K. Chesterson wrote about his detective "Father Brown". That story was about the attempt by a master thief named Flambeau to steal a very rare and valuable religious item. It is being handled and protected by Father Brown, and he succeeds in preventing the theft. The film actually does not follow the story to its actual conclusion: Father Brown confounds Flambeau and the head of the French Police, M. Aristide Valentin. Both men realize the Father's superior wisdom and bow to him at the conclusion of the story.
When the B.B.C. did the 1974 series of the "Father Brown" stories they did not do THE BLUE CROSS. Ironically, the follow-up story THE SECRET GARDEN was the last episode of the short series, and one of the most ironic of the tales. For it is one of the few sequel tales in the series (most of the other ones concentrate on Brown and the reformed Flambeau) to pick up on the fate of a character.
Chesterton as a future spokesman of Roman Catholicism could not but notice the active warfare (a realistic term) in France between the right wing political parties (most of whom supported the Catholic Church) and the left wing and center parties that supported religious freedom and freedom of thought by pushing for a non-sectarian school system (as opposed to one controlled by the Church). One can imagine from his writings he supported the antics of the right wing parties and their spokesman like Charles Maurras and Leon Daudet and (earlier) Eduard Drumont. So when the story unfolds in THE SECRET GARDEN, one can understand why Chesterton leads it to its bizarre conclusion.
M. Aristide Valentin, the Interior Minister (he's in charge of the police forces of France) is an atheist, and is constantly under attack by the right wing press (in the episode he is played by Ferdy Mayne, and he is first seen looking at a newspaper that shows him to have his head chopped off by a guillotine). He does have a heart, and has tried to get the President of France to grant clemency to a young man who murdered his wife after a drunken argument. But his enemies make sure that the President won't grant it. So he is forced to attend the execution, and come late to see his guests for the evening. These include Father Brown (Kenneth More) who is accompanying an American millionaire named Brayne (Peter Dynely), Lord and Lady Galloway (Cyril Luckham and Joan Benham) and their daughter Lady Margaret (Eileen Waugh), Valentine's mistress the Duchess of Mont St. Michel (Rosemary Dunham), Dr. Bernard Simon (Rowland Davies), and M. Valentine's assistant and secretary Beaumont (Stefan Gryff). There is also Commandant Neil O'Brian of the Foreign Legion (Charles Dance). The latter's appearance annoys Lord and Lady Galloway, for their daughter and O'Brian were lovers, and his political views did not gel with his Lordship's (who broke up the romance, and then saw O'Brian flee Ireland to avoid arrest).
Brown is involved with religious discussion from several angles during the dinner party - those of the atheists (Valentin, Beaumont, Dr. Simon, presumably the Duchess) - and those of the high Anglicans Galloways. His only ally appears to be O'Brian, although Brayne is there with Brown as his friend. But the Father maintains his cool, clear head against all arguments.
Valentin comes late but finally arrives, and subsequently a package is delivered for him. In the meantime Brown takes an interest in the mansions unique garden - a lush bit of greenery in the back surrounded by high walls (one of which faces the Seine). It troubles Brown, who tells the Doctor that he finds the wall somewhat unnerving as it closes off the people inside the house from the outside world.
After dinner the pressures of social and political life effect most of the guests. Valentin is concentrating on the right wing attacks on him. The Galloways are snubbing O'Brian, but also trying to keep their daughter from talking to him. Then Mr. Brayne (who had been admiring the arms on the wall) disappears. Shortly afterward a body of a beheaded man is found in the garden, but the head is of a total stranger. It is this mystery that Father Brown confronts and solves - producing one of the weirdest choices for a criminal one can imagine.
All the episodes of this all-too-short series were well produced, and they do capture the spirit of the period (roughly 1904 to 1926 or so) quite nicely. More with his gentle delivery made an ideal Father Brown, and one really wishes he could have done the entire series of stories rather than the one set that were turned out. Mayne captures the ennui of a politician at the end of his tether, wondering if his involvement in trying to help anyone actually caused greater evil. And Luckham (best recalled as Sir Christopher Mont in the original THE FORSYTE SAGA) has a good scene towards the end trying to understand O'Brian (Dance) and his beliefs and behavior. In the end his failure to come to grips with this causes him to lose more than he bargained for.