The Settling, by Simon Guerrier, takes the Seventh Doctor, Ace and Hex to Drogheda and then to Wexford in 1649, where, inevitably, they get mixed up in Cromwell's invasion of Ireland - Hex ends up as a confidant of Cromwell's, while the Doctor and Ace get involved with the civilian victims of the unfolding tragedy.
Doctor Who has, in general, almost no relationship with Ireland. The Irish characters in the entire TV canon can be counted on the fingers of one hand (Sean in The Underwater Menace, Flannigan in The Wheel in Space, McDermott in Terror of the Autons and Casey in The Talons of Weng-Chiang, with a generous half a finger for each of Chip in New Earth and Brannigan in Gridlock, neither of whom as characters can ever have been near Ireland). Irish people are less visible than black people in Who of any era; meanwhile entire stories are set (if not necessarily filmed) in Scotland and Wales.
It's not too difficult to understand this reticence, at least from the Old Who perspective. Doctor Who is, after all, an entertainment show, and for most of its run it was rather tricky to engage with Irish issues both tastefully and entertainingly. (Supporting evidence: So You Think You've Got Troubles, the unsuccessful sitcom starring Warren Mitchell as a Jewish businessman sent to Belfast.) A couple of the Pertwee novelisations mention the Northern Ireland troubles in the background; if any of the spinoff novels go there, I have not yet encountered them. Turning the focus around, Daragh Carville's magnificent play Regenerations (download link here) takes Sophie Aldred and Tom Baker to Belfast to bring peace both to the local Doctor Who fans and to the city more widely.
Guerrier's choice of setting for The Settling, therefore, is pretty brave. Making the story a pure historical tale is also pretty challenging - you can just play it for laughs (which can be done successfully - The Romans, The Crusaders, The Kingmaker and stretching a point The Unicorn and the Wasp) or, as Guerrier has done, go for the more risky didactic approach, more demanding of both cast and audience. This can fail miserably (eg The Marian Conspiracy), but it can work well - witness the early Hartnells, The Witch Hunters or The Council of Nicæa. It works here (though the inclusion of the bloke who is going off to found the Royal Society is a bit gratuitous).
Cromwell is one of the dividing points between me and many of my fellow leftie liberal friends from the neighbouring island. In England in particular, he is a liberal hero, having abolished the Divine Right of Kings and ensured the supremacy of Parliament. But for me it's impossible to separate that from his direct personal responsibility for the slaughter in Ireland. Guerrier makes a decent effort at reconciling the two sides of Cromwell in The Settling, and the play is carried by Clive Mantle as the man himself and Philip Olivier as the Doctor's Scouse companion Hex, discovering first that there is a human being behind his Irish grandmother's stories of terror and then that the stories of terror were true after all. Indeed, it's Olivier's best outing yet as Hex, with a framing narrative of him and Ace safely back in the Tardis, trying to talk through the trauma. It's a shame that, in sequence, it's rather overshadowed by The Kingmaker which was released immediately before - it's a lot better than the immediately following stories, with a bleak atmosphere of grief and savagery.
The history, of course, isn't perfect. Guerrier presents Drogheda and Wexford as the last Irish bastions of loyalty to the recently executed Charles I, which Cromwell therefore wishes to suppress, and while that's basically true, it's quite far from being the whole truth; both local and European politics, and in particular the religious/sectarian elements of the conflict, are rather underplayed. But one cannot expect too much detailed attention to the canvas of the seventeenth century in 100 minutes of the adventures of a roving timelord. The Settling is well worth a listen.