Lolita begins with a “foreword” written by Dr. John Ray Jr., the (fictional) editor of a manuscript written by the late Humbert Humbert while imprisoned for child sexual abuse and for murder. The foreword, which is in fact part of the fiction of the novel, serves as a frame story that provides context for Humbert’s narration and, in turn, infuses the narrative with dramatic irony. John Ray begins:
“Lolita, or the Confession of a White Widowed Male,” such were the two titles under which the writer of the present note received the strange pages it preambulates. “Humbert Humbert,” their author, had died in legal captivity, of coronary thrombosis, on November 16, 1952, a few days before his trial was scheduled to start. His lawyer, my good friend and relation, Clarence Choate Clark, Esq. [...] in asking me to edit the manuscript, based his request on a clause in his client’s will which empowered my eminent cousin to use his discretion in all matters pertaining to the preparation of “Lolita” for print.
Here, the (fictional) editor explains how he came into the possession of the “strange pages” that constitute the novel itself. “Their author,” given the pseudonym of “Humbert Humbert,” died in prison prior to the start of his trial. After Humbert’s death, his lawyer, Clarence Choate, sent the manuscript to Ray in accordance with a “clause in his client’s will” that the manuscript might be prepared for publication. This elaborate frame story sets up the (fictional) events of the novel as the “true” recollections of a deceased criminal regarding his life and crimes.
What's more, the details in this frame story create dramatic irony in the novel, since readers know from the outset not only that Humbert Humbert was imprisoned but also that he is no longer alive. The foreword also mentions what several characters from the narrative will go on to do in life, thus informing readers of things that the characters themselves—when they appear in the narrative—don't yet know.