On Sunday night the fourth season of "Downtown Abbey" drew to a typically dispiriting close with Mr. Carson and Mrs. Hughes enjoying a sudden, not entirely unexpected flirtation that led to a – brace yourselves – moment of discreet hand holding along Brighton beach.

Drama! (Well, it's not exactly "Baywatch," but that's half the point of this so slow-moving, it'd-make-hundred-year-old-turtles-look-like-sprinters show).

Which brings us to "Downton Abbey's" biggest enduring mystery: Tom Branson.  Why has the socialist Irish firebrand (played by the cast's most accomplished actor Allen Leech) decided that pig farming and pallid romantic uncertainty in England are where his future lies? As plot holes go, it's pretty cavernous.

As nearby Ireland is embroiled in the War of Independence and then the Civil War all of Tom's former political fire seems to have burned itself quite out.

Perhaps it's the procession of listless tea parties and dispiriting music recitals and turgid summer fetes that just drag on and on. Perhaps he's simply lost the will (losing wills is a recurring motif in the show, by the way).

In fairness, writer Julian Fellowes has allowed Branson a few unintentionally funny WTF moments where we see him ask himself what on earth he's still doing among these high born but ultimately pointless nobs now that his wife Lady Sibyl is resting in peace?

Once a chauffeur, Branson now wears expensive tweed suits and strolls around looking for inspiration to strike (or is that the show's writer?). It's simply not believable that a man of his passion would allow himself to drift when he has a daughter to raise and a cause to fight for.

Perhaps next season writer Fellows could remember that he has an extraordinarily talented actor to work with and an ideal opportunity to create an Irish foil to throw light on the doomed world of the English aristocracy.

Let’s hope he figures it out before the butler Thomas Barrow inherits the mansion and opens it as a summer park for working class tourists (you know that's how this story ends, right?).