(W.W. Norton; 216 pages; $24.95)

The extraordinary backdrop of author William Fiennes’ childhood was staged nearly 700 years before his birth, in 14th century England, when a moated castle began to be passed down through his father’s ancestors. While his parents confronted practical and financial ownership concerns, young William, a distant cousin of actors Ralph and Joseph Fiennes, had only to enjoy his enchanting fortress abode – the cynosure of his inspired second memoir.

At first glance, “The Music Room” is an ingenuous ode to Fiennes’ childhood. Because his parents viewed themselves as stewards of a historic site that should be shared with the world, they financed its upkeep by renting it out for community events, tours and uses such as shared garden plots. That meant Fiennes was often surrounded by a “parade of strangers,” and he regularly tagged along, beginning to “absorb the facts and stories of each room,” delighting that “Private: No Entry” signs didn’t apply to him.

His playground was the moat; he watched Shakespeare performed by theater groups in his backyard; he helped his mother water the rush matting in the King’s Chamber and he challenged himself to enter the scariest rooms. He let his imagination loose.

Yet Fiennes quickly pokes holes in this idyllic depiction by letting in its darker side; those fantasy years were haunted not by ancestors past but by the live ghost of his 11-year elder brother Richard, who suffered short-term memory loss, deteriorating mental capacity and other acute behavioral and cognitive effects due to frontal lobe brain damage from severe epilepsy. At that time, Richard and William were mental contemporaries, but whereas Fiennes knew his “childhood was a temporary predicament,” Richard’s was a different story. “His childlikeness was indefinite,” Fiennes writes. Like the castle itself, “he was moated in.”

Anecdotes revealing Richard’s frightening behavior punctuate and interrupt Fiennes’ otherwise dreamy and swirling narrative, just as the outbursts once disrupted family life. And in turn, Fiennes’ poetic prose is balanced by excerpts of scientific writings on the history of the brain and mind, which helped him understand that Richard’s lovable idiosyncrasies, such as his obsessive support of the Leeds football team, and times when “the threat of violence sharpened the air,” were all beyond Richard’s control.

As the narrative slowly advances, a seemingly limitless storehouse of lucid memories unfurl. Some loop in a rhythmic refrain of recurring daily events, such as “showing groups of students and tourists round the house, or arranging flowers in the Great Hall and Oak Room vases, or rubbing oil and wax into books, floorboard and armour.” In other instances, Fiennes grinds time to a near-halt, expertly bringing microscopic detail into focus: “enormous spiders roamed the pipework, emerging at night to spread themselves like starfish in the baths.” And often right in the midst of recollections, he moves seamlessly in and out of past and present tense, bringing readers directly into the past as if it were taking place today.

Early on, Fiennes plants a clever and apt metaphor for his creative narrative structure via his youthful fascination with his mother’s metronome, housed in the castle’s music room:

“Suddenly it seemed the time you set by the metronome was actual time, and that your life passed more slowly or quickly as you slid the weight up and down the scale, the music room a world that turned at whatever speed you judged appropriate. … The day’s pitch and time-keeping were in my hands.”

Fiennes writes that in his youth he never questioned “the world as I found it.” He also admits, “I didn’t question my brother’s seizures or the frightening and unpredictable swings of his mood from gentleness and warmth to opposition and violence – these too were just facts I grew up among, how things were.”

But here he resurrects, probes and preserves that time and place, finally meditating on how what one inherits – in his case, the castle and Richard’s illness – can define us, forever shaping our minds.