A thoughtful person is bound to pause occasionally and reflect upon the decisions that have shaped her life. The older that person gets, the more acute that curiosity is likely to be. How did she get to this point in her life, and what do past decisions portend for the years to come?

The narrator of "Memories of the Future," Siri Hustvedt's new novel, is having one of those moments. In August 1978, the 23-year-old known as S.H. makes a decision common to ambitious sorts with dreams of literary stardom: She "left the wide, flat fields of rural Minnesota for the island of Manhattan." Her goal: "To find the hero of my first novel."

Like a lot of writers, she kept a notebook. Thirty-eight years later, she found it, "packed neatly in a box of miscellany my mother had saved," as she and her younger sister moved their 92-year-old widowed mother into assisted living.

She also finds the novel she worked on during that year, an unfinished mystery about 14-year-old Ian Feathers, a "tall, skinny, smart, nearsighted, hyperlexic" fan of Sherlock Holmes who even had his own Dr. Watson: Isadora Simon, a classmate he met when they dissected a piglet in biology class.

Hustvedt is too smart to have turned this into a straightforward account of a year in the life of a budding artist. Like S.H.'s protagonist, Hustvedt knows a good mystery when she sees one, and what's a more compelling mystery, at least to an artist, than the way time Mobius-strips one's existence into a smooth, if mystifying, continuum?

The narrative alternates between S.H.'s reminiscences and diary entries from that year, excerpts from S.H.'s novel and Hustvedt's own illustrations.

Among the people S.H. meets in New York are Whitney Tilt, an "artist-poet or poet-artist," and Elena Bergthaler, an oft married socialite who hires impoverished S.H. to write her memoirs, a gig that allows S.H. to stop stealing sandwiches out of trash cans when she's hungry.

But the biggest influence is her next-door neighbor, Lucy Brite, whose chants about a brutal husband and a daughter who fell out of an apartment window penetrate the common wall. After Lucy rescues S.H. from an assault, the mystery of Lucy's life is revealed — a mystery as unnerving as the chants themselves.

The novel wanders in its more philosophical passages, and excerpts from S.H.'s novel don't feel fully formed. But "Memories of the Future" shines in its observations on the fluidity of time and the ways in which one's older and younger selves can coexist. Early in the book, S.H. notes that Einstein worried about "the problem of Now" and how it links past and future. That's a mystery Sherlock Holmes would have loved.

Michael Magras is a freelance book critic. His work has appeared in the Houston Chronicle, Pittsburgh Post-Gazette and Newsday.

Memories of the Future
By: Siri Hustvedt.
Publisher: Simon & Schuster, 318 pages, $27.
Event: 7 p.m. March 29, Magers & Quinn, 3038 Hennepin Av. S., Mpls.