Author John Grisham has written “The Tumor,” a fictional account of how a real medical technology could affect the future of medicine and is giving it away to spread the word. ( /www.fusfoundation.org.)

There are no lawyers or courtrooms in John Grisham’s new thriller. There is not even a single bad guy.

The protagonist is Paul, a 35-year-old suburbanite with a pretty wife, three beautiful children, and a tumor quietly swelling in his brain. One day his wife hears a loud thump in the bathroom.

“She finds him on the floor,” Grisham writes, “shaking in a full-blown grand mal seizure.”

And so begins “The Tumor,” one of the stranger literary digressions in recent memory. Against the wishes of his agent, editor and publisher, the author famous for (and rich from) legal thrillers, from “The Firm” to “The Rogue Lawyer,” just published a free book whose hero is a medical device called focused ultrasound.

Grisham says it’s the most important book of his career.

Billy Williams is the first patient in the world to receive focused ultrasound treatment for an essential tremor. A year after his procedure at the University of Virginia, he says he is "very, very happy" with treatment results. (Focused Ultrasound Foundation/Youtube)

“I write escapist popular fiction that entertains,” Grisham said in an interview. “It’s entertainment. It doesn’t pretend to be literature or anything else. But ‘The Tumor’ has the potential to one day save or prolong millions of lives.”

Focused ultrasound is a non-invasive treatment in development for cancer and other diseases that uses energy beams to destroy diseased tissues. How it became Grisham’s 38th book is a question many of his devoted readers have been wondering since it came out late last month.

“Huh?” wrote one reviewer on Amazon. Said another, “I really hope it stays free, because if people buy this, they will be very disappointed.”

Others have been surprised but more charitable, offering the sort of critical appreciation Grisham was hoping for. “Personally, I’m thankful John Grisham used his name recognition to educate me, an average Jane Doe,” one such reviewer wrote. “This is a prime example of how knowledge translates to power.”

And also how a powerful author can instantly raise the profile of a nonprofit foundation anxious to sway the medical world and regulators.

Grisham, 61, lives near Charlottesville, not far from Neal Kassell, a prominent University of Virginia neurosurgeon who founded the Focused Ultrasound Foundation in 2006. They became friends, inhabiting the same social circle and wine tastings. Grisham calls Kassell his “personal brain surgeon,” although he has not needed his services.

About eight years ago, Kassell asked Grisham to join the foundation’s board.

Best-selling author John Grisham. (Mitchell Layton/Getty Images)

“I told Neal I know nothing about medical devices or medical technology and I don’t really want to immerse myself in it,” Grisham said. “I went to law school. What could I add to the board?”

Kassell’s answer: raise awareness, which leads to raising money, which leads to influence. In 2014, the foundation spent $2.3 million on research and another $2.7 million on communications and advocacy, according to its annual report. This winter, it held two “reimbursement summits,” trying to persuade insurers to pay for the treatment.

But Grisham, despite his Southern charm and good-natured humor, wasn’t interested in pleading for cash.

“I’m not good at raising money,” Grisham said. “I don’t like to raise money. It’s been my experience that when I ask someone for money it’s not long before they return the favor.”

A few years ago, Grisham said he had a better, more organic way to employ his fame — by writing a book about the technology.

“I couldn’t think of a better way, in one fell swoop, to create awareness for this technology,” Kassell said.

But Grisham’s publishing industrial complex in New York was worried.

“They worry about everything,” he said. “That’s their job. They were worried a lot of readers would feel like they were deceived, that it wasn’t good for my brand. They are very protective of me.”

Grisham decided he didn’t much care, that the cause was worth any risk, and that his fans would tolerate his departure from legal thrillers, just as they tolerate his forays into young adult books and other projects.

He set aside time from working on his thrillers — he starts a new one every Jan. 1, finishing by July 1 — and went to work on “The Tumor,” whose title echoes many of his other books (“The Firm,” “The Pelican Brief”).

Grisham created Paul and the plot the way he always does.

“Writers are thieves,” he said. “We steal stories. We steal names. We steal scenes. We observe the world and we take what we need and modify it.”

In this case, the story and scenes weren’t overheard or imagined in courthouses or legal firms, but in long conversations over the years with Kassell.

“He tells stories like this all the time,” Grisham said. “A young person in the prime of life cut down and killed by a tumor. He’s seen the suffering. He’s been there. So I just went with it.”

The book is short, only 49 pages, and is available to download on Amazon or the foundation’s website. It includes illustrations, graphics and copies of brain scans, much like a promotional pamphlet at a doctor’s office.

By Page 10, Paul realizes he’s in serious trouble.

“When the neurosurgeon arrives early that morning for the initial consultation, he produces the [MRI] scan,” Grisham writes. “As they stare at it, Paul and his wife, Karen, are too stunned to speak. The doctor explains that Paul indeed has a tumor in his brain and it appears to be the type known as a glioma.”

The prognosis is grim. The only option is a dangerous surgery, which might get Paul another year, at most. Paul undergoes the surgery. Grisham describes the operation in clinical detail, with words — “dura mater” and “coagulation” — that don’t appear in his previous works.

After it’s over, the surgeon tells Paul and his wife to “plan for the average” — that he’d live for another year. Then the doctor leaves the room.

“Karen pulls the shades and turns off the lights,” Grisham writes. “They sit in the darkness, holding hands, as the monitors beep occasionally. When they speak, they discuss the best way to tell the children.”

Nine months later, in Chapter 4, Paul dies.

In Chapter 5, there’s a plot twist and a touch of magical realism.

“Paul was born in 1980, ten years too early,” Grisham writes. “Had he been born in 1990 and diagnosed with a brain tumor at the age of 35, in 2025, his story could be rewritten as follows . . .”

Paul has the seizure in the bathroom. He’s rushed to the hospital. This time, the surgeon offers focused ultrasound.

“He explains that the tumor in all probability cannot be cured and will return, but it can be controlled with repeated treatment,” Grisham writes, “giving Paul more years with a high quality of life.”

Paul is slid into an MRI machine, where “beams of ultrasound energy” are aimed at the tumor. Like a gotcha question near the end of a trial, it works. But the tumor eventually comes back. This time, he has the procedure again. And again.

The ending isn’t happy, but it’s hopeful. Grisham said he was careful not to give readers false hope. There have been plenty of promising cancer treatments to come along that have eventually failed.

“The tumor will eventually take Paul’s life,” Grisham writes. “With time, research, and improved technology, neurosurgeons are hopeful that a guy like Paul can live to the age of 45 or even 50, long enough to see his children mature.”

Paul gets seven more years. The foundation gets publicity. And Grisham gets the strange but moving satisfaction of writing a book that will never be a bestseller — and perhaps improving, not hurting, his valuable brand.

“Thank you for writing this,” one of his fans wrote on his Facebook page. “Wish this was available when my dad had brain cancer. I admire you even more.”