As I went room to room, turning off lights, I wondered about the history of our house, whether anyone had died in it. Even if someone had hung himself from the foyer chandelier, I couldn’t believe that he would be haunting the place. What’s believable and right in a work of allegorical fiction isn’t easily embraced in real life by a person of reason. I decided not to worry about it when I realized that my good dog’s tail had been wagging vigorously throughout her encounter; she had been enchanted by what she saw, and she wouldn’t be enchanted by a spirit with malevolent intentions.

A couple of friends have suggested that Trixie might have been following a moth in flight or some small winged insect that I didn’t notice. As lame as that explanation is, I considered it. But given how long the episode lasted and how many well-lighted rooms were on the tour, no moth or its equivalent could have escaped my attention.

Besides, Trixie never before or after that event was lured into the pursuit of any insect other than a few fine butterflies on summer days. And those butterfly chases were frisky, leaping exercises in doggy exuberance, nothing like the leisurely walk-around of the second floor that evening.

A number of people have told me stories about their dogs seeming to see things that humans can’t see, although none of their accounts were similar to mine. I do believe Trixie saw something that she found enchanting and that remained beyond my ken. I’ll never know what it might have been-unless in some other plane of existence I am reunited with her one day, and in that new world, she can talk.

During the almost eight additional years that we were fortunate enough to have Trixie, she never repeated that performance, and never exhibited any other kind of fey behavior. Nonetheless, I believe the moment was meaningful, revealing a special quality that cannot be easily defined but that was central to this dog’s uniqueness.

XIII a nose for trouble

EVEN SERIAL KILLERS have dogs they love and that return their affection, though it’s difficult to imagine John Wayne Gacy knitting a sweater for a Chihuahua or Jeffrey Dahmer taking time away from his collection of severed heads to frolic in the park with a Labradoodle.

Perhaps Stalin’s dogs had to love him or otherwise be shipped to a Siberian forced-labor camp, but no doubt they would have loved him without the threat of a life sentence to a Gulag. Consequently, we are not on solid ground if we insist that dogs are better judges of character than are human beings.

Yet I’ve heard people make this claim many times. And we have all seen movies in which only the dog recognizes that the new babysitter is a bug-eating psychopath or that the genial neighbor in the cardigan has been replaced by a shape-changing alien with an appetite for human sweetbreads.

Nevertheless, over time I learned that Trixie was an uncannily good judge of character with both humans and canines. While it’s true that she was people-oriented and liked nearly everyone she met to one degree or another, she seemed indifferent to about 10 percent of the people she encountered. She was not wary of or hostile to that fraction of humanity; she simply had little or no interest in them.

With the other 90 percent, her greeting always consisted of at minimum a grin and a wagging tail. The faster the tail moved, the more she approved of the person before her. About half the time, she raised her right forelimb and gently pawed at a new acquaintance as if to say, I’m here, see me, I like you, come down here where we can sniff each other’s face. This was a higher degree of approval than merely a grin and a wag. She expressed total acceptance by collapsing as if her legs had turned to rubber, rolling onto her back, and baring her tummy for her new friend’s admiration and attention.

The longer Trix was with us, the more I realized that the people to whom she presented her belly were the true friends with whom I, too, could leave myself entirely vulnerable without fear of attack. And those about whom she had mild reservations were also those whom I liked very much but felt I didn’t entirely know-although in my case, I would not be better able to discern the fine points of their character by sniffing their faces.

People whom I found to be cold or false, or in some other way off-putting, were without exception in the 10 percent toward whom Trixie remained indifferent. When these were individuals whom I had met previously, the argument could be made that from a score of subtle telltales in my demeanor and behavior, Trixie instantly read my opinion of the person and adopted it as her own. Dogs study us their whole lives and learn the meaning of our tiniest changes of expression and voice inflection. But when I met someone for the first time, Trixie’s opinion and mine also matched, though she instantly identified the troubling individuals as worthy only of indifference, while I needed longer to make the same judgment.

Only once did Trixie react so negatively to someone that she refused even to allow that person to touch her. I should have taken our golden girl’s warning seriously.

To protect the guilty, I will not indicate that person’s gender or occupation, and will use only the name X.

I knew X for the better part of a decade but only through a business relationship and from a distance. A couple of years earlier, before we were blessed with Trixie, X came to southern California with Y and Z, two people who worked for the company that employed X, and although they were not traveling on business related to us, Gerda and I took them all to dinner. The evening was not filled with the scintillating conversation and hilarity that might have made me want to say, “Let’s take turns flying across country once a week and do this every Friday night for the rest of our lives,” but we had a pleasant time.

When Trixie came to us, she was welcomed not merely as a pet; she participated in every aspect of our lives, including taking a role in my relationship with my most faithful readers. Those who live in the United States and write to me by snail mail have long received a twelve-page newsletter-Useless News-that informs them of forthcoming books but is largely about having fun, reprinting humorous pieces I’ve written. We began using photos of Trixie in the newsletter, adding funny captions. She wrote reviews of my forthcoming books, solemnly swearing that her praise could not be bought for cookies. Whenever a book failed to include a dog in at least a minor role, she gave it less than a five-star rating. I had so much fun creating Trixie’s singular manner of expression that eventually she would publish successful books “edited by” or “as told to” Dean Koontz.

As someone with whom I did business and as someone who claimed to read and like my books, X received Useless News and became a fan of Trixie. Eventually, X returned to California on a business trip, and we arranged a visit at the house before we went to lunch.

Usually, on hearing the chimes, Trixie bolted to the front door, eager to see who had come calling. This time, she hurried into the foyer as usual, but as I opened the door, she turned and scampered away so fast that X failed to get a glimpse of her.

I didn’t think much about this abrupt retreat. Perhaps she had heard someone open the pantry door in the kitchen, where her can of kibble was kept. She always assumed that no one could have any other purpose for entering the pantry except to get food for her.

I welcomed X into the living room, we chatted for a bit, and then I called upstairs to Linda to find out if Trixie was with her. Trix indeed had retreated to that office, and I asked Linda to bring her down to the living room.