Death in Paradise's field trip to London brings a special surprise (on top of the freezing weather and traffic noise that shocks Officer Dwayne Myers).
Why, yes! That is Father Ted's Ardal O'Hanlon serving as a Met police officer assigned to help out DI Humphrey Goodman and his team.
Ardal, 51, brings plenty of comedy to the role of DI Jack Mooney. There's a hint of Dougal about his character, but as Humphrey soon finds, Mooney's seemingly-irrelevant stories and anecdotes have a way of suddenly getting to the point: underneath his quirkiness he's sharp.
So what has Ardal been up to for the last few years, before he turned up in a dingy room at the Met Office – aside from his stand-up comedy career? Here's his TV CV:
Father Ted (1995-98)
The role of hapless, hopeless, childishly innocent Father Dougal McGuire has defined Ardal's career. This comedy about three Irish priests and their housekeeper became an unexpected hit, with co-stars including Dermot Morgan and Frank Kelly.
Big Bad World (1999-2001)
Ardal starred as journalist Eamon Donaghy. Unfortunately, despite running to three series, Big Bad World has been all but forgotten.
This Ben Elton comedy on the joys of new parenthood starred Ardal as a father out of his depth, struggling not to drown in nappies and cynicism. The cast included Mel Giedroyc as his wife, as well as Robert Webb and Sally Bretton as Bill and Mary Hathaway. Even Russell Brand was in it.
My Hero (2000-2006)
This superhero TV series featured Ardal as George Sunday, aka Thermoman – a dim-witted superhero from the planet Ultron. George was his human alias, but he struggled to fit in with life on Earth. The BBC sitcom had a decent following with Ardal at its helm, but he left after five series and was replaced by James Dreyfus for the final series.
Doctor Who (2007)
Ardal played Thomas Kincade Brannigan in a 2007 episode opposite David Tennant's Time Lord. Brannigan was a Catkind (humanoid feline) who lived in New New York. He and his wife were trapped on a motorway for 12 years, travelling only five miles - but he stepped in to help the Doctor who was looking for the vehicle containing his companion, Martha.
Val Falvey TD (2009)
This gentle political satire from Father Ted writer Arthur Mathews was a loving but bitter account of life in provincial Ireland. Ardal played Val, an inept, corrupt man who entered parliament on the strength of his family name. It only ran for six episodes and never really got off the ground.
London Irish (2013)
This sitcom followed the lives of four expat Northern Irish 20-somethings in London. Ardal played Chris "Da" Lynch, father of two of the twenty-somethings, Conor and Bronagh Lynch.
Nelly & Nora (2015)
Ardal lent his voice to the part of "Dad" in this CBeebies animation. It's not the first time he's been a voice actor: you can also hear him as Robbie the Reindeer.
After Hours (2015)
This Sky comedy drama starred Georgina Campbell, James Tarpey and Jaime Winston. Ardal played Peter Hannigan, whose son befriends two radio presenters running an internet radio station from a boat.
Death in Paradise airs at 9pm on Thursdays on BBC1