It took novelist Brian Morton decades to realize that he didn't always have to say yes to his mother. "It can take the better part of a lifetime to learn that you don't actually always have to be so damn good." Welcome to "Tasha: A Son's Memoir," Morton's bracing account of his late mother's final years.

Morton's novels — including the beautiful "Starting Out in the Evening," which became an equally fine film starring Frank Langella — all have in common a calm, caring voice that imbues the prose with a wry, pained tenderness, as if shaking its head at the human folly it describes. That same voice sustains this memoir, opening with the startling image of Morton's 85-year-old mother's car slowly filling with water, stalled in a terrible rainstorm en route to a granddaughter's dance recital.

Dramatically, Morton cuts to an early memory of himself, age 4, and his sister, 7, watching his mother jump from a moving train — luckily, not hurt too badly.

It's a useful reference. Morton had known that his mother was hellbent on driving to the recital, storm or no. But, he writes, "I'd learned long ago that when I tried to talk her out of doing something she was intent on, I had no chance."

This stalemate defines the grown son's lifelong predicament. Stakes now, however, have soared: The storm event causes his mother to have a stroke, which precipitates a steady decline that she denies almost every step of the way. Morton's burden looms: "I had successfully kept her at arm's length for many years ... and this was comfortable for me." That distance, he knew, was about to change. "I might have to call on different capacities in myself, and I didn't want to."

Checking her into a rehab hospital, he's touchingly hopeful: "Everything that can be fixed, we'll help her fix. ... The small stroke could be a turning point."

Alas, Tasha refuses "the audiologist, the urologist, and the shrink, and although she keeps going to physical therapy, she won't take it seriously." She won't let Morton remove a single swizzle stick from her junk-laden, cat-feces-and-dead-mice-riddled house. Morton must take her driver's license. She stops changing her clothes; her senior center peers complain. (She remains "almost feral in her refusal to even look at us. ... My mother's mind was alien to me now.")

Alternately furious with or covetous of Morton's care, she can still sometimes bristle with logic, as when arguing with a nurse about God's existence: "So [life's atrocities are] like a TV show to [God]? A TV show that he doesn't really like but he doesn't turn off?" At that, Morton can't suppress his pride, nor his laughter.

"How can you see your parents clearly?" Morton wonders. He's not sure he'll ever be able to, but to his extreme credit, he gives it everything, passionately chronicling his mother's knotty past — daughter, wife, widow, mother, teacher, union activist — interleaved with his own present exhaustion, exasperation and anguish (at one point Tasha wanders down the highway on foot in the middle of the night).

Caregivers for elderly parents may be stunned — also slightly relieved — to recognize various elements: desperate research, trial after trial (some, involving abusive caregivers, go shockingly wrong) and rage chased by guilt. Then there are the hopeless efforts to persuade the afflicted elder to consider assisted living and the grim realities in many such facilities.

Morton observes: " 'Being Mortal' [by surgeon/author Atul Gawande] is a book about how we treat the old. A book like this ... will make you aware of the very few places where things are done right, which always turn out to be too far away to be of help to you." And: "When you're taking care of an elderly parent, life is filled with ... situations that make what-ifs inevitable ... in which you have to decide how much you should demand and how little you can settle for."

Truth: I found "Tasha" addictive. I couldn't even slow down. Why? Its startling details, fearless depictions and the curiosity this sparks: How might Morton "solve" the unsolvable? Best is Morton's witty, scalding honesty — noting his fear, when a phrase suddenly eludes him, "of my own dementia to come."

"I love you," he tells Tasha at one (typically) hapless moment.

"I always knew that," she replies. "But it doesn't help."

A complex, arduous yet satisfying reckoning seeps through. Morton finds his mother's diary, and he discloses passages that let us better understand her loneliness, occasional resentment of her grown children and helplessness in the face of waning energy.

"People grow tired. She grew tired." Morton also honors his parents' better selves, their encouraging his choices to write and teach. "Tasha" stands as both a cri de coeur and vibrant testament — the painstaking, brave, generous piecing-together of a wildly difficult puzzle.

Joan Frank's newest novel is "The Outlook for Earthlings." Concurrent works are "Where You're All Going: Four Novellas" and "Try to Get Lost: Essays on Travel and Place."

Tasha: A Son's Memoir

By: Brian Morton.

Publisher: Avid Reader Press / Simon & Schuster, 208 pages, $28.