Each of the past two summers arrived with a treat from Stephen King: his version of a hard-boiled detective mystery. This year, the series culminates with a third and final volume worthy of its popular, page-turning predecessors.

What started in 2014 with the Edgar Award-winning “Mr. Mercedes” and continued last year in “Finders Keepers” reaches a pitch-perfect denouement in End of Watch. Returning for one final encore are King’s ragtag investigators: retired policeman Bill Hodges, whose suicidal tendencies have been curbed, but who is also still haunted by the perpetrator of earlier attacks; the mentally fragile, socially awkward and acutely perceptive Holly Gibney; and Jerome Robinson, a teen-age tech wiz and neighbor now doing volunteer work in Arizona during a hiatus from college.

Bill and Holly, who still live in the unnamed Rust Belt city where the previous stories were set, became partners in a private-detective agency over the course of the previous novels. In “End of Watch,” they discover Brady Hartsfield, the twisted killer rendered comatose in “Mr. Mercedes,” may have found a new way to make people kill themselves. Though it makes the experience richer to have read the earlier novels, “End of Watch” also works just fine as a stand-alone book.

King has developed such a comfort level with his characters that the story slips into an immediate, fast-paced rhythm without a hiccup. As with so many of King’s stories, the chugging plot rises on his ability to combine narrative drive with a sense of how ordinary people might think and act in the face of extraordinary situations.

And some of the best moments come when the characters reflect on the quotidian while wrestling with larger worries and fears.

“Hodges tries to swim below the pain and stay asleep, but it pulls him up steadily until he breaks the surface and opens his eyes,” King writes of the retired detective’s as-yet unknown health ailment, a distraction from the distraction of figuring out an improbable series of suicides. “He fumbles for the bedside clock and sees it’s two AM. A bad time to awake, maybe the worst time. When he suffered insomnia after his retirement, he thought of two AM as the suicide hour.… Two in the morning. The hour when it seems daylight will never come.”

Of another character, King describes his military service as “touring Afghanistan, all expenses paid by the United States government.”

The three books cover a span of seven years, starting with Brady Hartsfield’s massacre that leaves eight people dead while standing in line at a job fair during the heart of the recession in 2009. “Mr. Mercedes” – spoiler alert – told that story and ended with Brady suffering extensive brain damage. Since then, Bill Hodges has been obsessed with the idea that Brady is somehow recovering his mental capacity while pretending to still be in a coma.

As that notion haunts Bill and Holly, a common thread emerges in the suicides: an attachment among each of the victims to a defunct GameBoy-type handheld video-game player. Meet the Zappit, a device with an old-school motif that proves hypnotic – and, in some cases, soul-killing.

Credit King for rolling out a chilling, and plausible, recipe for Internet-fueled hysteria. Combined with a whiteout winter storm, a tick-tock race to stop mass detonation, and nail-biting near-misses, “End of Watch” roars to a satisfying conclusion.

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Which leads to another intriguing mystery: What’s next for the King of Horror? He is, at age 68, riding a late-career surge that, in the last decade, includes stellar story collections (“Just After Sunset,” “Full Dark, No Stars,” and “Bazaar of Bad Dreams”), an epic alt-history novel (“11/22/63”), an epic apocalyptic tale (“Under the Dome”), a dazzling sequel to “The Shining,” and the Bill Hodges trilogy. For most, that output would mark a great career. For King, those are just part of his past 10 years of very industrious work.

To which I can only say: Long live the King.