Talking about his new novel, Warlight (Knopf, May), author and poet Michael Ondaatje compares his writing method to archaeology. His work usually begins with a fragment or an image, which he uses to slowly uncover the story. For Warlight, Ondaatje began with a sentence that became the novel’s opening line: “In 1945 our parents went away and left us in the care of two men who may have been criminals.”

“It seems ridiculous and a bit like a kind of fairy tale,” Ondaatje says. “I knew nothing more than that when I began the book. Even the post-WWII era came later. I sort of discovered that was the time. I wasn’t setting out to write a war novel or a postwar novel; that became the landscape.”

Ondaatje says he finds the story as he researches and writes—like an archaeologist carefully brushing dust and grit from an artifact. “I think most of the energy spent on writing a book is used to discover what the story is,” he adds. And, like archaeology, it’s painstaking work.

Ondaatje says it usually takes him about five years to write a novel, and he handwrites most drafts. “I don’t really know the characters before the book is written—they’re not fully formed yet,” he explains, saying that he needs to “live with the possibilities of characters for a period of time.”

In fact, Ondaatje continues, “I really begin a book not knowing what it is going to be about, to be honest, though it sounds rather foolish, but that’s the way I’ve worked in the past.” That past includes his best-known work, the 1992 novel The English Patient, which won the Man Booker prize, as well as six other novels; his most recent The Cat’s Table (2011). He has also written 15 books of poetry.

Ondaatje, 74, was born in Sri Lanka and spent his early childhood there. He lived in England from 1954 until he immigrated to Canada in 1962. He is a longtime resident of Toronto, a city that featured prominently in his historical novel In the Skin of a Lion (Knopf, 1987). But when I reached him by telephone, he and his partner, author Linda Spalding, and their family were escaping the last bluster of the long Canadian winter at a rented retreat north of San Francisco, a landscape that became part of the setting for his 2007 novel, Divisadero.

Warlight is set in England, where Ondaatje lived as a teen. After his initial idea for the story took hold, he says, the city of London materialized as he focused on what it must have been like there following WWII. (The title comes from the time of blackouts and curfews during the war, when lights had to be dimmed to hide the city’s features from German bombers, but could metaphorically reflect the secrets and hidden history within the postwar plot and the characters’ lives.)

Ondaatje’s research took him to many places along the Thames, but he says that character serves as his engine in writing a novel. And it is 14-year-old Nathaniel Williams who opens Warlight as he describes his parents leaving him and his sister, Rachel, who is nearly 16. The parents tell the children that they’re going to Singapore, where his father has accepted a new job. Separations of that kind weren’t unusual in wartime, Ondaatje says. But one of the children’s guardians, a man they call the Moth, later admits to Nathaniel that his mother, Rose, didn’t go to Singapore. Nathaniel’s efforts to solve the mystery of where his mother has gone, as well as why she left, drive much of the novel.

It is also a bildungsroman following Nathaniel as he begins to explore the world beyond his family. A new sort of family begins to takes shape in the house, loosely led by the Moth and his friend, whom Rachel and Nathaniel name the Darter, and an odd assortment of guests dropping in.

The Moth guides Nathaniel into his first jobs, working in the laundry and then as a dishwasher in London’s grand Criterion Restaurant, where he learns to navigate the adult world. In the kitchen of another restaurant, he meets his first love. Later, the Darter recruits Nathaniel to help him transport illegal racing greyhounds—dogs with no racing pedigree that had been smuggled into the country—on barges on the Thames. “We passed industrial buildings,” Ondaatje writes, “their lights muted, faint as stars, as if we were in a time capsule of the war years when blackouts and curfews had been in effect, when there was just warlight and only blind barges were allowed on this stretch of the river.”

There is an abrupt and surprising shift into Nathaniel’s adult life in the second half of the novel. Rose has reappeared, and Nathaniel has learned that what took her away was some dangerous work for British intelligence. They now live a secluded life in the Suffolk countryside, far removed from the hustle and bustle of London. But Rose is secretive by necessity, and so the second half of the book also follows Nathaniel’s attempts to decipher his mother and her life and to make sense of his own.

Almost everyone in the book goes by pseudonyms. Rose nicknames Nathaniel and Rachel as Stitch and Wren, respectively. Even Nathaniel’s teenage lover asks him to call her Agnes, but it isn’t her real name. Ondaatje says, “That wasn’t something I planned to do consciously, but two-thirds of the way through, I realized this was happening.” Ondaatje recalls someone observing a similar phenomenon when he was writing In the Skin of a Lion, pointing out that nearly every character is an immigrant. He appreciates such accidents, speculating that “if I planned it ahead of time, it might be too odd or too schematic.”

Though Ondaatje says much of the book is a story about a family, the affairs of the world and political intrigue also rush into it when Rose reappears. She had been a radio operator during the war, and later she intercepted, altered, and re-sent German signals. The war is officially over when this story begins, but “no wars end punctually,” Ondaatje notes. “There’s always a postwar period that is kind of scary because it is violent.”

Rose tries to escape the violence, seeking anonymity in the Suffolk countryside where she grew up. “It is a book about the human consequences more than the political and strategic things,” Ondaatje says. “I read a lot about that, but I was more interested in why Rose was away.”

Rose demonstrates Ondaatje’s skill in creating complicated and all-too-human characters. Rachel renounces Rose for abandoning her and Nathaniel. But holding Rose up to the light, readers may see a bad mother or a war hero, self-interest or self-sacrifice; it all depends on the perspective. Nathaniel has his own contradictions and questions to answer, as do so many of Ondaatje’s characters.

“I love them all,” Ondaatje says, confessing that he can’t help feeling nervous sending them out into the world. But they have been in good hands, and now his readers are, too.