How are readers being confronted with mysterious facts throughout the story that are not explained until the end? What are these mysterious facts and how does the author prolong the suspense until a big reveal at the end? Conan Doyle: "The Purloined Letter," "The Sign of Four," "A Scandal in Bohemia," The Hound of the Baskervilles, "The Speckled Band," and "The Copper Beeches." Dick Donovan: "The Jeweled Skull" G. K. Chesterton: "The Eye of Apollo" E.C. Bentley: "The Inoffensive Captain" Agatha Christie: And Then There Were None, Mysterious Affair at Styles Ngaio Marsh: "Man Lay Dead"

Many of these tales contain mysteries that are not solved until the end and in which readers are confronted with confusing facts that represent "red herrings" (or devices that lead the readers to false conclusions). An example is Agatha Christie's And Then There Were None. In this mystery, eight strangers are brought to an island off the coast of England, where they are greeted by two servants. They listen to a recording accusing them each of different crimes by a host known as "U.N. Owen," which the guests recognize as standing for "unknown." Everyone on the island is killed in succession.
Scotland Yard detectives arrive to solve the mystery, and they conclude that the killer was still alive on the island after killing his last victim, as the chair that the last victim had used to hang herself was neatly placed against the wall. However, the detectives are unable to solve the mystery. The mystery is not solved until a confession note washes up on shore some indeterminate time later, in which the killer, Justice Wargrave, explains that he had the help of another victim to fake his own death and kill the others. The killer states that without this confession note, Scotland Yard would never have been able to solve the crime. In addition, the reader is never given the clues to solve the mystery; instead, Christie withholds information, and the reader is not privy to the clues necessary to solve the crime.
In Conan Doyle's "The Speckled Band," the reader is also presented with confusing and misleading clues. For example, Helen Stoner fears that Roylott, her stepfather, is threatening her life as she is about to marry. Two years earlier, Helen's twin sister was killed, and Helen heard her sister complain of loud noises before her death. When the sister died, she uttered the words "the speckled band." The reader has no idea what these clues mean until Sherlock Holmes and Watson spend a night in Helen's room and find a poisonous snake, the speckled band, going into Helen's room through a ventilator shaft. Holmes later reveals that Roylott would have lost the fortune his wife had left him if Helen had married, so he tried to kill Helen (and did kill her sister) with the snake. It is only at the end of the story that these explanatory details are revealed to the reader. In both of these stories, Christie and Doyle without information from the reader that is only revealed at the end. You can also find other stories from this list that fit this description.