If you've ever owned and loved a pet, you know that their stories always have sad endings. That said, "A Big Little Life" by best-selling suspense author Dean Koontz is as happy as it gets in the pet world.

Subtitled "A Memoir of a Joyful Dog" (Hyperion, $24.99), it's the story of Trixie, the golden retriever owned by Koontz and his wife, Gerda. In her short life here, Trixie brought them love, companionship and a greater understanding of the way that good works in the world.

"Trixie made us much more joyful," said Koontz in a phone interview. "Dogs can change your life if you let them. People write to me, 'My dog has done these things, but I never paid attention to them before.' I tell them, 'Pay attention.'"

All pet owners think their pets are the greatest, but Koontz knows Trixie was unique: perhaps heaven-sent, maybe even ---- an angel. Early in the book, he describes an event that hints at Trixie's special being, and continues to show how she was different from other dogs.

Trixie was a graduate of Canine Companions for Independence, a nonprofit that trains companion and assistance animals for the disabled. Koontz encountered the group while researching his book "Midnight," and he and his wife became supporters. CCI, in turn, had long urged them to take one of their "release" dogs ---- dogs that retire from the program or who otherwise can no longer be a part of it.

Because of elbow surgery, Trixie retired from CCI at age 2 1/2 and was adopted by the Koontzes. There she reigned for her 12 too-short years, passing away in 2007; but her influence has extended far beyond her mortal span. While Trixie was with the Koontzes, she became the author (through Koontz) of several cheery books of canine philosophy.

"Her first book ('Life Is Good') outsold my first hardcover book," Koontz recalled. "There was some jealousy around the house for a while."

The Trixie line also includes a line of products at Petsmart, a calendar and two children's books, starting with the just-released "I, Trixie Who Is Dog." (Trixie tends to ignore superfluous words. "She cuts to the chase," said Koontz.) And she's got her own Web site. All author's proceeds from Trixie products benefit Canine Companions.

"Short Stuff (one of her nicknames) has become a conglomerate," Koontz writes in "Big Little Life." "Gerda and I break into smiles every time we think about what a long shadow this little dog has cast even after moving on from this world."

"Big Little Life" is about the love between a dog and its owners, but it also tells other stories: about Koontz's less-than-lavish childhood with a violent, alcoholic father; meeting and wooing Gerda; his rise to fame and fortune as an author who has sold more than 400 million books.

When Trixie enters their well-ordered life, the Koontzes find a new awareness and appreciation of life's funny, touching and mysterious moments. And when the inevitable happens, readers will share their grief ---- and be consoled by a message of a greater purpose and plan in the universe.

That spiritual aspect is a large part, but not obtrusively, of "Big Little Life." Because of Trixie, Koontz said, "I took the plunge to more spiritual writing, more humor ---- she gave me the courage to do it.

"It's one reason I wanted to write this book. If you relate to your dog not just as a pet, but as a companion, you begin to see an intelligence, and a moral attitude."

Was Trixie really an angel? "I can't say," said Koontz. "It's the ineffable. But there are so many examples ... people saying, 'she's really special.' There's a feeling in your heart of what the truth is. I can never know, but I do know she completely changed so many things. Trixie was a theophany" ---- a manifestation of God.

Before Trixie, Koontz said, he had encountered his share of unscrupulous people, betrayals and outright treachery that "had just made me cynical. But the dog made me start opening up again to the beauty of the world. Trixie brought that back to me. She brought back a lot of happiness, and I got back to where I used to be."

Contact staff writer Laura Groch at lgroch@nctimes.com or 760-739-6658.

Dean Koontz will be appearing at 11 a.m. Saturday at the Dean, Gerda and Trixie Koontz campus of Canine Companions for Independence, 124 Rancho del Oro Drive, Oceanside, to sign "A Big Little Life" and also Trixie's children's book, "I, Trixie Who Is Dog." Author's proceeds from both books will be donated to CCI. Campus tours and demonstrations begin at 9 a.m. Call 760-901-4300.