If weight is to be given to prolific output as well as to literary excellence, it would be no stretch to claim that America’s greatest mystery writer is Robert B. Parker.

There is, admittedly, a similarity between one book and another, but one could say the same about Charles Dickens, William Faulkner, and Raymond Chandler. The thing is, if you like one book, you’re sure to like them all, which is no small accomplishment.

Another prolific mystery writer — and also one of my all-time favorites — is Rex Stout, who shares a significant trait with Mr. Parker: Neither of these relentlessly entertaining authors was overly concerned with constructing original and complex plots, yet both created iconic detectives whom we never tire of encountering between the covers of one of their satisfying adventures.

Having read all (I think) of Mr. Stout’s Nero Wolfe novels, and almost every one of Mr. Parker’s Spenser stories, I would be hard-pressed to recall with accuracy the complete plotline of any book by either author, although certain scenes still echo through the halls of time: Wolfe deciding he needed to exercise, and taking up throwing darts, which he called javelins; Spenser spurning a beautiful and very naked terrorist in “The Judas Goat” because of his fidelity to the love of his life, Susan Silverman. The new novel, “Now and Then” (Putnam, 296 pages, $25.95) begins as readers have come to expect a Spenser novel to begin. A potential client walks into Spenser’s office, needing help. They get off on the wrong foot when the client has attitude but no sense of humor, unlike Spenser, who has plenty of attitude but is very funny.

Now, I confess to a having a great affection for Spenser’s smart-aleck dialogue. My wife insists that’s because he speaks the way I would if I were a little quicker off the mark and a lot wittier.

Here are the first lines spoken.

“You Spenser?”

“And proud of it.”

“Are you being a wise guy?”

“Only for a second.”

Maybe it’s not for everybody, and if you don’t think this is funny, you may not like the Spenser series, because there are a lot of exchanges like that, with strangers and with those to whom he’s close, especially Susan, who is herself no slouch in the wisenheimer department. Philip Marlowe spoke that way, and so did Lew Archer, and Spenser belongs in their company.

Anyway, the poor slob thinks his wife is behaving strangely and wants Spenser to find out why. The detective assumes she’s cheating on him. “I don’t think she would do that to me,” the client says. “Maybe it’s not about you,” Spenser replies. Guess what? She is cheating, and rather blatantly, too. Spenser gets proof in the form of an audio tape that is only slightly more explicit than the latest issue of Hustler. In addition to the dirty parts, the tape records evidence of Last Hope, a terrorist organization run by a smarmy Lothario, Perry Alderson. When three people are shot to death, Spenser quickly learns that this is more than the garden-variety marriage-gone-south scenario. After delivering his accounts of the evenings of the straying spouse, Spenser’s job is done. He no longer has a client. But he wants to know more about Alderson, the head of Last Hope. It’s his white knight thing, and he doesn’t know any other way to be. When asked why he has to chase this case, Spenser says, “Because I can’t sing and dance.” In an “interview” with Spenser that Mr. Parker once distributed, Spenser is asked why he does what he does. “There are a lot of problems which need to be solved, and their solution takes the kind of skills I have,” he answered.

With an entire terrorist organization as an adversary, even Spenser’s skills may not be enough to survive, or to protect Susan, so he calls on his personal cavalry: Hawk, a regular player in Spenser’s cases, plus a few other tough guys. When he needs to go out of town to investigate Alderson’s history, the only person on earth Spenser would trust to guard Susan is Hawk.

Maybe someday there will be a novel in which Susan, Hawk, or Spenser doesn’t make it — a time when the odds are just too overwhelming, even for this charismatic and heroic trio. If it happens, I hope it’s not in my lifetime, since I don’t want to lose these beloved figures from my own life.

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.