Charming Billy spans three generations of Irish Americans living in Queens, New York, from World War II to the end of the twentieth century. The narrator, whose first name is not given, is the grown daughter of Billy's best friend and cousin, Dennis. She has come home to support her father after Billy is found dying in the street. She begins the story at a funeral party in the Bronx, in 1982, where forty-seven friends and relatives have gathered to mourn and to reminisce about Billy Lynch.
Dennis takes charge of the arrangements for Maeve, Billy's widow, making sure that the party runs smoothly. The narrator begins her description of Billy, an alcoholic who greatly taxed those who loved him, which includes everyone in the room. At this point, Dennis's daughter shares the narrative with various members of the party, who offer their personal memories of Billy.
Their talk turns to Eva, the girl whom Billy loved first and hoped to marry. He met her one summer on Long Island after he and Dennis returned from the war. Eva had been helping her sister Mary with her duties as a nanny for a wealthy family on the island. At the end of the summer, Eva went back to Ireland with Billy's ring to wait for him to have enough money to send for her. After taking on a second job, Billy sent $500 to her. Kate, Billy's sister, remembers that Mary called Dennis soon after and told him that Eva had died of pneumonia, which Dennis then relayed to Billy. It was a blow that the relatives thought he would never endure.
Eventually, he met and married Maeve, whom many thought would be his salvation, but the narrator notes that she "was only a faint consolation, a futile attempt to mend an irreparably broken heart. A moment's grace, a flash of optimism, not enough for a lifetime." They then discuss and argue about his drinking, which increased over the years into full-fledged alcoholism. His sister Rosemary insists alcoholism is a disease and so was not a result of his weakness, but Dan Lynch argues that he would not have drunk himself to death if Eva had not died, noting that Billy had told him "that every year was a weight on his shoulders."
At the end of the party, Dennis admits to his daughter, "Here's the most pathetic part of all. Eva never died. It was a lie." He then takes over the narrative to tell Billy's story, moving back and forth from past to present. He explains that what Mary had actually told him was that Eva had married her hometown sweetheart and kept Billy's money to make a down payment on a gas station. Dennis, fearing that Billy would be devastated by that news, determined that it would be easier for him to think that she died than to know she rejected him for another man.
Dennis tells his daughter that Billy found out that he had lied when Billy decided to make a trip in 1975 to Ireland, where he found Eva married with four children. He admits to her, "it's a bad business. A lie like that," and notes that neither he nor Billy ever told anyone the truth about Eva. Dennis then describes how...