This is the ultimate primary source for the private life of one of the towering figures of nineteenth-century Ireland. Parnell, for those of you who need reminding, built a coalition between parliamentarians and terrorists to force the British government of the day to improve the conditions of Ireland's tenant farmers, and had managed to get Gladstone to promise Home Rule - an autonomous government for Ireland - when his leadership of Irish nationalism suddenly collapsed after it was revealed that he had been the lover, for ten years, of the wife of one of the MPs representing his party. They married after her divorce, but he died suddenly only three months later, at the age of 45.
This is her story. Katherine was the daughter of an ordained baronet; her brother won a VC; her mother and sister wrote novels; she gives a rather entrancing picture of her childhood and courtship by William O' Shea. Their marriage quickly went sour, but he had meantime introduced her to his party leader, and it is implied that they became lovers while she was nursing him in 1880, during a convalescence from one of his frequent illnesses. (One of the great questions of Irish history is "What if Parnell had lived thirty years longer?" - but on the evidence here that would have been very unlikely.)
She doesn't go into much intimate detail about her life with Parnell - there is a lovely moment of frolicking on the beach at Eastbourne, and a poignant death scene - but does reproduce a very large number of Parnell's letters and telegrams to her, and goes into enough detail about her own role as an intermediary between Parnell and Gladstone in the early to mid 1880s to make it clear that Gladstone knew full well of their relationship, and that his publicly expressed shock when it came to light in 1890 was pretty bogus. She also gives some of her correspondence from her first husband, Captain O' Shea, in which he appears completely self-obsessed and very unpleasant; a stark contrast with Parnell's tenderness towards her combined with a political single-mindedness.
Anyway, you wouldn't want to read this as a jumping-off point to this period of Irish history, but if you already have a background knowledge of the main events it's pretty fascinating. Incidentally one of the popular pubs near my office in the European Quarter of Brussels is called Kitty O'Shea's after the author; she herself always went by "Katie" to friends and family (and, mysteriously, was called "Dick" by her first husband), but popular lore remembers her differently.