There is a particular kind of tribute that goes beyond craft — the moment when an actor stops performing and begins, in some deeper sense, to inhabit. For Catherine Corless, the amateur historian from County Galway whose painstaking research exposed the fate of nearly 800 children buried in unmarked graves at the Tuam mother-and-baby home, that moment arrived when she watched Monica Dolan on screen and recognised, with a start, something that felt unmistakably like herself. Dolan, an English actress perhaps best known to audiences on both sides of the Atlantic for her work in BBC dramas, was required to do considerably more than master a Galway accent — though Corless, with characteristic directness, confirms that she did even that very well. What distinguished the performance, in Corless's telling, was the willingness to go further: to absorb the emotional texture of years of solitary effort, of doors that opened slowly and doors that did not open at all.

"She went to the extremes, really, to get the feeling and the emotion I went through and the struggle," Corless has said, and the word extremes carries in it a kind of quiet wonder. "She portrayed me just as myself." The film, which was awarded Best Irish Film at the 38th Galway Film Fleadh in July, opened in Irish cinemas on 25 September and is scheduled to reach UK audiences on 9 October — a release pattern that moves, almost symbolically, from the country where the story was buried to the one that governed it for so long.