When neurosurgeon Henry Marsh's third memoir opens, he has volunteered to take part in a study that requires a scan of his brain.

"It seemed a bit of a joke at the time," he writes in "And Finally." But weeks later, when the scan arrives in the mail, he puts off looking at it. Now 70 and retired, he understands that his brain might not appear as fresh and healthy as he would like to believe it is.

Given his age, he knows, "My brain is starting to rot." Looking at proof of that "is just too frightening."

This is one of the many compelling themes of this serious and wise book — how powerful denial is in the human brain, and how all of us, even physicians, can ignore uncomfortable truths.

As it turns out, Marsh's brain was not what he needed to be worried about. An array of dire symptoms, disregarded for years, eventually leads to a diagnosis of advanced prostate cancer.

By ignoring the signs, "I thought I was being stoical when in reality I was being a coward," he says. "I simply couldn't believe the diagnosis at first, so deeply ingrained was my denial."

For people in his profession, Marsh notes, the world is divided into two camps: doctors and patients. Moving from one camp to the other is painful — the doctors no longer treat him as a peer and he's reduced to googling his symptoms just like the rest of us. The hospital feels different, more intimidating and impersonal, and as he heads to the radiotherapy department, "I could feel myself lose height as I walked along the corridor."

In his 2017 memoir, "Admissions," a finalist for a National Book Critics Circle award, Marsh wrote about life on the cusp of retirement. He had bought an old cottage in Oxford that he was fixing up in hopes of moving there from London. But in "And Finally," he notes that his repairs were substandard, the house needs more work than he could manage, and, "I wasted too much time and energy in my determination to do everything myself, and too many of the roofs I have built leak when it rains."

It is impossible not to read this as a metaphor for his life. And yet there is nothing depressing about this book. Marsh's tone is measured, clear, sometimes wryly humorous, as he looks at himself, his foibles, his mistakes and decisions.

He is unflinching when he describes the changes that cancer and its treatment cause in his body — the occasional incontinence, the "chemical castration" that shrinks his tumors but also causes him to fatten up and lose his hair, giving him — a lifelong runner, who cycles everywhere — "the plump and hairless body of a eunuch."

Marsh also deftly weaves in other issues — his love of nature, his grandchildren and his unending fascination with the mysteries of the human brain.

What is consciousness? How do billions of nerves make us us, with thoughts, desires, personalities? "Answering one question just opens the door to a room with yet more doors."

And though Marsh also makes a case for assisted dying (he has a suicide kit, but doubts he will use it), this book is firmly an ode to life. "I so long not to die!" he says. "The wish to keep living remains as intense as ever."

I wish Marsh all the best with his cancer treatments. But rest assured, this book, written with passion and curiosity, makes clear that there's absolutely nothing wrong with his brain.

Laurie Hertzel is senior editor for books at the Star Tribune.

And Finally

By: Henry Marsh.

Publisher: St. Martin's Press, 240 pages, $27.99.