Of all the unexpected visitors my family received over the holidays, there was probably no soul more unlikely than Vietnam Santa. Forty years ago, my parents and sister had gone out one night just before Christmas, leaving me alone. I was 16, and I'd managed to make some unfortunate decisions, winding up goofy on a cocktail I'd invented that contained equal measures of Virginia Gentleman bourbon and orange Hi-C. Also, I had invited over a girl I barely knew, who'd arrived intending to make out with me but who had instead passed out in a guest room on the third floor.

As she slept, I sat down at the piano in the living room and began to play. I blew into a microphone that was not there, and said, "Thank you, Philadelphia. Thank you." Then I played the opening riff of Simon and Garfunkel's Mrs Robinson. The crowd in the Spectrum went wild.

That was when the doorbell rang. I got up and swung open the door, and there he was: white beard, red suit, bottle of Jack Daniel's in one hand.

"Santa?" I said. I was not thrilled to see him. I still had the problem of the passed-out girl upstairs to solve. St Nick wasn't going to make things any simpler.

"Are you St George?" he asked. This question wasn't as deranged as it seems, given that the family that had lived in our old house before us, the Hunts, had a child named St George, as well as another one named Al, nicknamed Hoops, who later became a well-regarded journalist. The Hunts used to have a legendary party every year, the Saturday night before Christmas.

I told him who I was. I also explained that the Hunts did not live there anymore. "Dr Hunt died," I said.

"Oh," said Santa. "I been away. Vietnam and all." I nodded. The year before had been full of images on the news of the POWs returning from Hanoi. "You want something?" I asked him. I figured I could make him one of these Hi-C things.

"Nah," said Santa. "I just figured I'd stop in. They'd been having this party for 25 years. I thought about this party a lot when I was over in Nam and all." I asked him in, and soon Santa was sitting in the love seat. I went back to the piano and started up again. "Look around you, all you see are sympathetic eyes." As I sang it, he sat there drinking, and his eyes shone.

There had been other night visitors. On a snowy Christmas Eve in 1966, my parents were already in bed when the bell rang. My sister and I swung open the door to see a tall bald man standing there without a coat.

"Do you know who I am?" he said. "I'm your Uncle Al." We'd seen him only once or twice before. My mother said "he had his troubles", which included, but were not limited to, a mysterious dark-haired woman who had broken his heart. He spent a lot of time travelling the country on boxcars, moving between the poles of Stone Harbor, New Jersey, on one coast, and Treasure Island, California, on the other. My sister and I invited him in. We heated up some leftover chicken a la king for him, and as we did, he told us stories and showed us how to make a paper cup by folding a piece of notebook paper. He also drew a picture of a Canada goose. Later, he played the harmonica for us, which he had to do very, very softly so as not to wake the grown-ups.

We gave him a blanket and he slept on the couch by the Christmas tree. At dawn, I half expected Uncle Al to have disappeared, but there he was, drinking black coffee. The world was covered in snow. I felt bad that we didn't have any Christmas gifts for Uncle Al, but he said he didn't mind.

I could name another half-dozen people who turned up unexpectedly on Christmas Eve over the course of my life. In 1986, a few months after my father died, my friend Kenny showed up unannounced. He cooked for us, cleaned for us, and broke up our routine in the wake of that loss.

I've received a lot of gifts over the years, from things as wonderful as a telescope and a home beer-making kit to things as lachrymose as a broken toy soldier. But the best present of all, of course, is the presence of other souls. If grace is the gift that cannot be asked for, but can only be received, then perhaps there is no greater grace than the gift of those whom we did not expect.

"What's that you say, Mrs Robinson? Joltin' Joe has left and gone away. Hey, hey, hey." I finished up. There was a moment of silence, then Vietnam Santa applauded. "Sounds all right, kid," he said, and put the cap back on his whiskey. "Well, I gotta go. Merry Christmas, and all." He headed off.

Years later, I learnt that Vietnam Santa had, in fact, not been to Vietnam at all. He was actually one of the Hunt boys, cleverly disguised as Santa, who, after all those years, just wanted to have one last look inside the house he'd grown up in. While I was playing Mrs Robinson for him, his mother and another one of the brothers were out in the car in our driveway.

Later, I climbed to the third floor to find that the girl upstairs had woken up. "Hey," she asked me. "Who was that at the door?"

NEW YORK TIMES