NEW YORK (NYTimes) - The unnamed narrator of Spy Of The First Person, the final work by playwright Sam Shepard, suffers from a degenerative disease that leaves him immobile, disconnected from his own body but keenly, painfully aware of his surroundings and his meandering consciousness.

"Nothing seems to be working now. Hands. Arms. Legs. Nothing. I just lie here," he writes. "Waiting for someone to find me. I just look up at the sky."

A second narrator watches the ailing man, with curious detachment, as he struggles to win control over his unruly limbs: "He eats cheese and crackers all day. Iced tea. He sips on that. But he has particular trouble with his hands and arms, I've noticed. His hands and arms don't work much. He uses his legs, his knees, his thighs, to bring his arms and hands to his face in order to be able to eat his cheese and crackers."

Shepard wrote the book in the final months of his life, when his health was rapidly declining from amyotrophic lateral sclerosis, or Lou Gehrig's disease.

He had always been incredibly private, and he didn't want to publicize his deteriorating health. When he died this July at his home in Kentucky, at 73, few people apart from his family, closest friends and collaborators knew about his diagnosis.

But Shepard explored his condition through his writing - in vivid, precise prose that transformed his worsening symptoms into something akin to poetry. He wrote in notebooks at first, as he always had, but when his condition grew more grave and he could no longer control his hands, he dictated into a recorder.

The resulting work, which Knopf will publish Tuesday, is an unvarnished, intimate portrait of a man facing the end of his life, as he reflects on his past and observes how his own body has betrayed him.

"He's watching himself as his life is ebbing away, and what Sam does with this experience as it's happening to him is turning it into this incredible prose," said LuAnn Walther, Shepard's longtime editor, who worked with him on about 20 books. "It's so direct, and it's so emotional and haunting and moving."

Shepard was best known as an actor and playwright - he appeared in more than 50 films and wrote 55 plays, including True West, Fool For Love and the Pulitzer Prize-winning Buried Child. But he also frequently experimented with prose, and liked pushing genre boundaries, mixing autobiography with fiction.

With Spy Of The First Person, he again blurred the line between fiction and memoir. He was adamant that he didn't want the book to be categorized as a novel, even though his publisher told him that could create marketing problems. "He said, 'Why does anybody need a label?'" Walther said.

Walther first learned that Shepard had Lou Gehrig's disease - a neurodegenerative disease that affects the nerve cells in the spinal cord and brain - in fall 2015. He had just finished a new manuscript, a work that he published in February.

He alluded to his condition in the book, titled "The One Inside," months before it would become public, in a passage that was so brief that Walther said she read right past it.

"Something in his body refuses to get up," he wrote. "The appendages don't seem connected to the motor - whatever that is - driving this thing. They won't take direction - won't be dictated to - the arms, legs, feet, hands. Nothing moves. Nothing even wants to. The brain isn't sending signals."

When Shepard began working on Spy Of The First Person in early 2016, he could still write by hand. But a few months later, as his illness worsened, that became impossible. So his daughter, Hannah, bought him a recorder, and would set it up by him and leave him to dictate in the garden of his home in Kentucky. When he was ready for a break, he would signal to her, and she would come and turn it off. His sisters, Roxanne and Sandy, transcribed the tapes and gave the pages back to him to read over.

"His mind was like a steel trap," his sister Sandy Rogers said. "He would dictate for an hour and a half or two hours from the top to the bottom, and he would never change anything."

Shepard blended fragments of the past with the present, as he often did in his plays. In one chapter, the narrator, who seems to be addressing his children, says that "there's some things you don't know about me mainly because they happened before you were born," and recounts his time living in a condemned building in downtown Manhattan.

Later, he describes going out to a Mexican restaurant with his family, pushed in a wheelchair by his sons Jesse and Walker: "I'll never forget the strength I felt from my two boys behind me," he wrote.

"He wanted them to know how much he loved them," Rogers said of Shepard's children. "He knew what was happening." The process felt foreign to him at first. The tools he had always relied on - his pen and his typewriter - no longer served him. Instead of writing in solitude, as he was accustomed to, he needed near constant physical assistance.

Shepard gave his family members specific instructions on how he wanted the book to be published, and even chose the cover image, an eerie black and white shot of an older man staring up at circling birds, by photographer Graciela Iturbide.

One of the most moving moments in the book occurs before the story even begins. In a heart-rending inversion of a typical dedication page, where the author often thanks his or her family, Spy Of The First Person is dedicated to the author himself: "Sam's children, Hannah, Walker and Jesse would like to recognise their father's life and work and the tremendous effort he made to complete his final book."