Any attempt to say with certainty, "This is the plot of Finnegan's Wake" would be blasphemy because the language in which the book is written defies any attempt at certainty. It is for all intents and purposes barely English, but by reading the novel, one adapts to the language. This is the generally accepted summary from literary authorities who have worked to understand it:
The novel begins mid-sentence ("riverrun, past Eve and Adam's...). We learn about a neighborhood near Dublin called "Howth Castle and Environs." Right off, Finnegan dies, falling down a ladder. His wife serves his body as the main course at his own wake, but he mysteriously vanishes. After short, seemingly unrelated vignettes, there is a fight, and someone accidentally spills whiskey on the casket, and Finnegan again emerges for a last drink. They talk him into dying and finally giving up the drink.
In prose that verges on a dream of the sublime, we meet the Earwicker family. The father, HCE, has become smeared by a local rumor which threatens to destroy the family's reputation. The rumor is that he molested a couple of young girls in a park. HCE's wife, ALP, works to correct their appearance, writing a letter. In the meantime, their two sons, Shem the Penman and Shaun the Postman, are locked into an Oedipal dispute about who is their mother's favorite, and how they might go about replacing their newly-disgraced father as head-of-household. The plan culminates in their father admitting guilt, although it is unclear what these confessions are supposed to mean.
ALP finishes her letters and Shaun the Postman sets about delivering them, running into a talking donkey, akin to Balaam's donkey. Shaun struggles to understand and relay the meaning of his mother's letters. He encounters a medium who summons the spirit of his (apparently dead) father who relays yet another opinion about what happened. Meanwhile, Mr. and Mrs. Porter are trying to make love but are constantly interrupted by children with archetypal nightmares. They finally find the time, and as they finish, the rooster crows.
The novel ends with a short chapter of (again seemingly irrelevant) vignetters. ALP is offered a chance to end the novel, and she reads from one of her letters. The exit soliloquy runs long, and she stops to try and wake her husband. She is incarnated as an important Irish river (yes), and runs along into the ocean. The last line of the sentence, is first half of the first sentence of the book: "A way a lone a last a love a long the"
