There was a time when you knew where you stood. You went to the bookstore and bought a fantasy novel, and there would be wizards, mythical creatures, and impossible occurrences. If you bought a mystery, you were going to have a crime, suspects, clues, and a detective who solved it using rational thought processes.

Now and then, there were exceptions, with apparently supernatural events usually exposed as fakery by a detective whose job it was to fearlessly enter the twilight zone of ghosts, demons, and psychic phenomena, as chronicled in such books as “Carnacki, the Ghost-Finder” by William Hope Hodgson, “John Silence, Physician Extraordinary” by Algernon Blackwood, and several volumes about Simon Ark by Edward D. Hoch.

Later, there was the occasional phenomenon, such as “Falling Angel” by William Hjortsberg and “The Lovely Bones” by Alice Sebold, which mixed supernatural elements with detective stories. But recently the floodgates appear to have been opened, as, in a single week, the best-seller list featured three novels that combined these previously disparate genres. On the hardcover list were Jodi Picoult’s “Change of Heart” (Atria, 447 pages, $26.95) and Jim Butcher’s “Small Favor” (Roc, 420 pages, $23.95), while the paperback list included Michael Chabon’s “The Yiddish Policemen’s Union” (Harper Perennial, 416 pages, $15.95), which previously had appeared on the hardcover list.

Few authors outsell Ms. Picoult, who has found a formula that works well for her and for her readers: Assemble a large cast of clearly defined characters, give them a lot of short chapters in which to tell the story from their point of view, and add important social issues that inform and intensify conflict.

In her new book, those include such subjects as the death penalty, bioethics, religion, child abuse, and prisoners’ rights. June Nealon lost her husband when a drunk driver killed him, but she remarries, only to have her new husband and her young daughter murdered. The killer, Shay Bourne, is brought to trial, convicted, and sentenced to death. The reader has to accept the plot element that a priest was on a jury that voted to send Bourne to death row, and, furthermore, that he then becomes Bourne’s spiritual adviser.

June was pregnant at the time of the murders, her daughter born with a faulty heart that will kill her before long. Bourne offers to have a heart transplant to save the girl: Since he is scheduled to meet his end via lethal injection, his heart will no longer be viable, and he asks to be hanged instead. Naturally, the ACLU leaps in to protect his rights — against his wishes.

What further complicates matters is that Bourne bears an uncanny likeness to Jesus Christ, as described in the Gospel of Thomas, and miraculous events occur in the prison: A dead bird comes back to life, a terminal AIDS patient is cured, and wine flows from a water faucet. If being willing to suspend disbelief in the face of all reason is an act of generosity, call me Scrooge.

Mr. Butcher has had great success with his series about Harry Blackstone Copperfield Dresden, a Chicago wizard who works as a private detective. In “Small Favor,” the ironically titled 10th episode in “The Dresden Files,” the Winter Queen, Mab, asks Harry for a “small” favor that puts his life and that of his family in danger.

Mab wants Harry to rescue the kidnapped Gentleman Johnny Marcone, one of Chicago’s most notorious gangsters, a human monster who wants to exert greater control over the local extra-normal population.

The wizard’s efforts are rebuffed by Titania, the Summer Queen and Mab’s sister, who sends vicious Billy Goats Gruff to stop him. They have cute names, but are more dangerous than monkeys with guns.

Although “The Dresden Files” are described as detective novels, and there is a Chicago cop as a recurring figure, they are total fantasies with too much weirdness for the detective genre.

By contrast, there is Mr. Chabon’s excellent novel, which was nominated for an Edgar as a mystery and won a Nebula as a fantasy, partially earned by creating a history that never was, in which the world’s Jews migrate to Alaska to form their own country. Although we know that this never occurred, it all feels far more realistic than Ms. Picoult’s prison or Mr. Butcher’s Chicago.

In spite of Mr. Chabon’s outstanding effort, I’ll continue to prefer my mysteries the way private eyes prefer their bourbon: straight.

Mr. Penzler is the proprietor of the Mysterious Bookshop in Manhattan and the series editor of the annual “Best American Mystery Stories.” He can be reached at ottopenzler@mysteriousbookshop.com.