Barry Martin was a construction foreman, the man in charge of getting building projects off the ground and into the air.

His new contract, back in 2006, was just like any other: a massive shopping mall in his home town of Seattle.

Not much of a reader, Martin started the job unaware there was already a fly in the ointment. The local press was making a big story out of the fact that a lady in her mid-eighties - "who looked like a bulldog with wire-framed glasses" - refused to sell her house, no matter how much the developers offered. So feted was she that the opening scene of Pixar's movie Up! was inspired by her predicament.

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Happily for her, the house did not take flight. While a neighbourhood was pulled down around her to make way for cranes and girders, Edith Wilson Macefield looked on unperturbed from her tidy front garden and continued to put out seed for the birds. This old house was where she'd lived for decades, and where she planned to die - as her mother had, on the battered couch in her living room.

At the start of any project, Martin tells us in his conversational but zippily told memoir, he goes around those in the vicinity of the works, giving out his card in case people need to contact him. This he did with Edith. Call me if you need anything, he said.

Frail but feisty, Edith became friends with Martin, who was touched by her courage and tenacity. He also found her fascinating. Her house was lined with books, and she revealed she was a writer. More facts emerged. She had been a spy, working in Nazi Germany. And the mother of dozens of adopted Jewish children. Never sure how much of her history to believe, Martin reflects, "Looking at Edith was a little like looking at those books: a million stories hidden in there."

The day she called him to ask if he could drive her to the hairdresser's their relationship entered entirely new waters. Soon Martin was doing her shopping and cooking her dinner each night. As time went on, and Edith needed almost full-time attention, Martin became her carer. His wife and two children barely saw him. Some nights, driving back from Edith's, he had just reached home when she called him back. Increasingly, her demands, and her utter dependence on him, consumed all the hours he had.

Cast at first as the evil developer trying to trick Edith into selling her house, Martin was revealed as a tender-hearted man whose patience and charity, if this story is to be believed, are exceptional. Not that he would put it like that. The running theme throughout the three years he knew Edith is that of the strain of juggling his job, his family and this exceedingly heavy responsibility.

"I started feeling like I was living in two different worlds. There was this public perception, in which Edith and I were part of some big play with big themes, a play about preserving the past and about the evils of progress. And then there was the day to day world, where it was just Edith and me, living our lives."

Nor is he trying to seem like a saint. "I think when you're taking care of an old person and everyone's telling you what a great sacrifice you're making, what you're really thinking is 'it might seem that way, but I'm drawing this selfish little line in the sand, and come hell or high water I am not going to let this old lady cross it'." For him, that line usually involved a fishing trip.

Edith could be playful, and she could be nasty. On rare occasions, Martin lost his temper, but he always went back. Abandonment was her biggest fear. That and being put in a care home.

Written with the help of journalist Philip Lerman, former national editor of USA Today, Under One Roof is a schmaltzy but affecting work, marinated in American sentiment, and underpinned by a folksy philosophy of doing the right thing.

The David and Goliath theme of the house being dwarfed by the huge mall soon melts into something far more interesting. Under One Roof is the portrait of a man unable to walk away from someone who needs him, and of a woman who has reached an age when most find it easier to forget she is as much an individual as they are. Though to the end her house remained rooted to the ground, this, as Pixar realised, is a truly uplifting story.