By Michael M. Thomas

March 11, 2001 | 7:00 p.m

The morning of Sunday, Feb. 18, was, as always, bright-but

for the first time since we'd arrived in Jamaica, the wind was sufficiently down and the sea calm enough for decent snorkeling. Beloved Stepmother was in good spirits. The night before, we had attended the annual party at Round Hill that benefits the associated charities of Hanover Parish, which had gone well, although Poppi did complain of having been sideswiped by a particularly aggressively mixed margarita. Poppi, Peggy O'Shea and I donned flippers, etc., and set out for our favorite spot-a small reef that lies approximately 100 yards offshore from the site on which Poppi and my father built their vacation house back in 1959-60. It's the place where, along with her native Engadine, she felt closest to Nature and thus happiest. We swam about for a while, then headed in, Poppi leading the way. When she reached the tip of the rocky breakwater that guards our little beach, the first shock hit her. My eldest son Jeffrey, sitting on the beach, saw there was trouble; he and my daughter-in-law Laura ran to her aid, and helped her into the shallows, where Laura supported her while Jeffrey ran to phone for assistance. By now, I had seen that something was going on and rushed in, as did Ricky, the gardener. When I got to her side, it was clear she was leaving us. For no more than a couple of minutes, we were frozen there, like a Pietà by Mantegna or Giovanni Bellini. She was calm; she wasn't confused, and I don't think she was in much pain. "I'm going," she murmured, and then, seconds later, "Nigel will know what to do"-a reference to Nigel Pemberton, our oldest Jamaica chum-and then she was gone. Thus ended the most extraordinary association of my life, and, I dare say, of the lives of a great many others. When Poppi came into my life, in 1949, I was a month away from entering eighth grade. When she left it, I was two months to the day short of cashing my first Social Security check. That kind of span deserves thinking about. She was the sort of person you should only think about in terms whole and straightforward. Frequently, when the fog of death settles on the landscape of a life, all that remains to be seen are the shining peaks, and that's what we talk about among ourselves or from the lectern at memorial services. This was a lady, however, whose fascination lay in her fullness. Especially for me, because the "step-" relationship is never less than complicated, and needs to be worked at full-time from both ends. I think of our half-century together as being like a flight above her beloved Alps in a small plane: frequently bumpy, but never less than breathtaking. She was born to command. A joke in our family is that, in all the years we knew and loved her, there is one phrase that none of us ever heard pass her lips: "Now, what would everyone like to do today?" Some years ago, in St. Moritz, when I had done something that didn't fit her book, I received the following interesting phone call: "Herr Thomas, here is Ernst at the Palace Hotel. Frau Poppi says I should tell you to go jump in the lake!" The day after she died, the flags flew at half-mast above the Corviglia Club, as they did at Tryall. She was about the last of the Old Guard at what was once the most glamorous, stylish, fun resort in the world-and the most beautiful-and with her passing disappears all but the final vestige of something that I doubt can ever be recaptured. Once again, I think of the words written on the retirement of Ty Cobb, which I paraphrase: "We will not see her like again, for the game has changed-and not for the better." She was probably the best friend anyone who could fairly claim her friendship ever had. I have known a lot of people in my life, but never one who went to bat for her friends with the unflagging, even ferocious zeal of my Beloved Stepmother. A doctor's daughter, she had a special feeling for those whose lives weren't going well, who had less: less money, less health, less to fight with. It was old-fashioned noblesse oblige, if you will, the duty that goes with privilege or comparative advantage, an obligation to look out for those at whom fortune either scowled or smiled too thinly for her liking. She was an American citizen, naturalized as soon as she could be after her marriage to Joe Thomas, and I think she understood-as well as anyone I can think of-the injunction James Fenimore Cooper lays on his countrymen in The American Democrat , which I have "re-gendered" to fit: "Liberality is particularly the quality of a gentlewoman …. She asks no more for herself than she is willing to concede to others. She feels that her superiority is in her attainments, practices and principles, which if they are not always moral, are above meanness, and she has usually no pride in the mere vulgar consequence of wealth." Of course, Poppi famously extended these principles to include animals, whose cause she championed unremittingly, personally and institutionally. She liked to tell me that animals were every bit as interesting as humans, but she was also willing to admit doubt; five years ago, after a Wildlife Conservation Society trip to Africa where we were privileged to be tutored by George Schaller, the great zoologist, she confessed that the behavior of New York society women at close quarters on safari was every bit as bloody-toothed terrifying as anything we had seen in the savannas of Ngorongoro. In the last few months, if it is any consolation, Poppi's outlook darkened. Not that she let on in public; her friends counted on her to be there for them , after all, not to tell them her troubles. But there were medical issues whose long-term effects promised to be dire. Old friends were dying at an unacceptable rate. Life was getting to be too much. Several times she spoke to me of a wish to pass on. And so she did. In the whole sense of things, I cannot honestly say I wish it had been otherwise-and I, thank God, was there with her at the end. I will go to my own grave convinced that she realized what was happening, that she saw in a flash that this was how easily and swiftly it might end, and that she added a bit of afterburner of her own to speed herself on her way. I'm happy for Poppi. She got pretty much the life she wanted, and she definitely got the death she wanted: quick, in a place she loved, surrounded by people who cared deeply for and about her. Still, no matter how grateful I am to the powers who so considerately arranged for her to take her leave in this way, I have to say this. Three years ago, as many of the family as could be rounded up gathered in Jamaica. Four generations were represented. This coming August, when Poppi would have been 86, there will be three. The diminution seems insuperable, insupportable, unacceptable.