TENANTS HARBOR — Barbara Walsh figured the worst that could happen was he would say no.

In truth, she hardly expected any response at all. She assumed Jamie Wyeth probably would just blow her off. No way the famous painter would take the time to illustrate her children’s book about the death of the family dog, she said to herself.

“But a friend persisted. She insisted, ‘Call Jamie.’ I thought, ‘Oh, sure — and I’ll go to the moon, too,'” Walsh said.

Walsh, a veteran newspaper reporter who has made many awkward phone calls in her life, dialed Wyeth directly. Not only did he take her call, but he was kind to her. He encouraged Walsh to share with him what she had written.

“Send me the book,” he assured her. “I’ll take a look.”

Months passed. Walsh rewrote and tweaked her story endlessly, all the while without a peep from Wyeth. Then one day, a letter arrived at her Winthrop home, her address printed with a flourish of bright blue ink.

She opened the envelope expectantly, and was thrilled and surprised to read that Wyeth wanted to explore collaborating further.

The result of their effort is “Sammy in the Sky,” a new children’s book that Massachusetts-based Candlewick Press published this week. It’s a gripping and honest story about how one family coped with the death of a beloved family pet.

Both Walsh and Wyeth will sign copies of “Sammy in the Sky” from 1 to 4 p.m. Wednesday at the Farnsworth Art Museum in Rockland. The event, which is free, will take place in the museum’s Victorian garden, on Elm Street between Main and Union streets.

The title refers to Sammy’s place in the clouds, where good dogs go to chase bubbles after they die. The book stars Sammy, Walsh’s loyal hound, who died in 2003. The co-stars are Walsh’s daughters, Emma and Nora, now 13 and 10, respectively.

The story is told from Emma’s perspective in the first person, although she is not named in the book.

In an interview at his home in Tenants Harbor, Wyeth said Walsh’s manuscript made an immediate and lasting impact on him. He’s illustrated a couple of children’s books before, and he receives frequent requests to do more. But he’s busy enough with his painting career that he simply can’t take the time required to do justice to a book.

This one was different.

“Barbara’s writing is very effective,” he said. “The story absolutely rang true for me. A dog’s death affects me much more than a person’s death.”

His illustrations convey the range of emotions in Walsh’s story — the joy of companionship, with Sammy gleefully licking the little girl’s face, and the thrill of the chase as he bounds after gulls on the beach.

The difficult emotions are present too — the uncertainty in Sammy’s eyes when the family learns he is sick and dying; the trepidation of the girl as she hugs her dog just before he dies; the undulating waves of grief upon his death and the pensive confusion that follows the morning after.

“The next morning, Daddy and I went for a long walk on the beach,” Walsh writes. “I searched for Sammy in the sky. I searched and searched for a cloud that looked like Sammy. I looked for his face, his paws and his big brown eyes.

“‘Can’t Sammy come back?’ I asked Daddy. ‘Just for a little while?’

“Daddy shook his head. ‘You’ll have to remember him in your heart,’ he said.

“That night, I dreamed of Sammy. I felt his whiskers tickle my cheek, his cold nose nuzzle my hand. When the dawn light filled my room, I reached out to hug Sammy — but then I remembered he was gone.”

Wyeth labored over the illustrations, and treated each as a separate painting. The book includes nearly two dozen paintings, which Wyeth completed in gauche and watercolor over the course of many months.

He took a few minor liberties with Walsh’s story. He didn’t try to re-create his girl in Emma’s image, and instead found a model to help him in the painting process. He outfitted the little girl in a pair of blue overalls, which Emma typically would not wear. He gave her sister blonde hair, which isn’t accurate either.

Wyeth haggled back and forth with Candlewick editors about other details. “It wasn’t always smooth sailing,” he said.

But he held his ground and prevailed on the issues that he cared most deeply about, ultimately telling Candlewick, “I’m not an illustrator. If you want an illustration, go find someone else.”

Because of his insistence, the book’s pictures convey the emotions of Walsh’s story: love, joy, grief and reconciliation.

During the interview at Wyeth’s home, Walsh said, “I knew Jamie’s work would be stunning. But I was so impressed with his ability to handle the emotions.”

Wyeth interrupted, telling her, “Your emotions and the words were just so powerful.”

He said he appreciated Walsh’s story because it wasn’t safe, easy or soft. She took her story all the way to the most challenging spot in the range of human emotions, “which was right down my alley. Barbara wrote it in such a way that it has impact and emotion. She did a wonderful job.”

An avowed dog lover, Wyeth saw no point in toning down the pain of loss.

“The dog dies. People get sad,” he said. “Animals mean a lot to me. I spend more time with animals than I do with people. Animals are almost always loving and kind.”

In his dedication, he said he illustrated the book, “For all the dogs I have loved and lost.”

“Sammy in the Sky” is Wyeth’s third picture book. His others, “The Stray” and “Cabbages and Kings,” came many years ago. He did his work for “Sammy in the Sky” in honor of his late grandfather, the legendary illustrator N.C. Wyeth, whose work Jamie adores.

This is Walsh’s first book. A second, “August Gale,” is due this fall. It is a memoir geared toward adults.