But there was lots of message left — the MOM, the meat of the message, a mishmash of symbols and concepts that had been established earlier, each one tagged with several numbers. Nobody could make sense of it.

The breakthrough came on a Sunday evening. At Chez Halifax, Sunday nights were Scrabble nights, when Don and Sarah sat on opposites sides of the dining-room table, the fancy turntable set that Sarah had bought him many Christmases ago between them.

Sarah didn’t like the game nearly as much as Don did, but she played it to make him happy. He, meanwhile, had less fondness for bridge than she did — or, truth be told, for Julie and Howie Fein, who lived up the street — but he dutifully joined Sarah in a game with them once a week.

They were getting near the end of the Scrabble match; fewer than a dozen tiles were left in the drawstring bag. Don, as always, was winning. He’d already managed a bingo — Scrabble-speak for playing all seven of one’s letters in a single turn — making the improbable wanderous by building on his previous de, one of the many two-letter combos that Scrabble accepted as a word but that Sarah, in all of her forty-eight years, had never seen anyone actually use as a word. Don was an expert in what she called Scrabble babble: he’d memorized endless lists of obscure words, without bothering to learn their meanings. She’d given up long ago challenging any string of letters he played. It was always in the Official Scrabble Players Dictionary, even if her trusty Canadian Oxford didn’t have it. Still, it was bad enough when he played something like muzjik, as he had just now, with both a Z and a J, but to get it on a triple-word score, and—

And suddenly Sarah was on her feet.

"What?" said Don, indignant. "It’s a word!"

"It’s not just the symbol, it’s where it appears!" She was heading out of the dining room, through the kitchen, and into the living room.

"What?" he said, getting up to follow her.

"In the message! The part that doesn’t make sense!" She was speaking as she moved. "The rest of the message defines an… an idea-space, and the numbers are coordinates for where the symbols go within it. They’re relating concepts to each other in some sort of three-dimensional array…" She was running down the stairs to the basement, where, back then, the family computer had been kept. He followed.

Sixteen-year-old Carl was seated in front of the bulky CRT monitor, headphones on, playing one of those damned first-person-shooter games that Don so disapproved of. Ten-year-old Emily, meanwhile, was watching Desperate Housewives on TV.

"Carl, I need the computer—"

"In a bit, Mom. I’m at the tenth level—"

"Now!"

It was so rare for Sarah to yell that her son actually did get up, relinquishing the swivel chair. "How do you get out of this damn thing?" Sarah snapped, sitting down.

Carl reached over his mother’s shoulder and did something with the mouse. Don, meanwhile, turned down the volume on the TV, earning him a petulant "Hey!" from Emily.

"It’s an X-Y-Z grid," Sarah said. She opened Firefox, and accessed one of the countless sites that had the Dracon message online. "I’m sure of it. They’re defining the placement of terms."

"On a map?" Don said.

"What? No, no, no. Not on a map — in space! It’s like a 3-D page-description language. You know, like Postscript, but for documents that don’t just have height and width but depth as well." She was pounding rapidly at the keyboard. "If I can just figure out the parameters of the defined volume, and…"

More keystrokes. Don and Carl stood by, watching in rapt attention. "Damn!" said Sarah. "It’s not a cube… that’d be too easy. A rectangular prism then. But what are the dimensions?"

The mouse pointer was darting about the screen like a rocket piloted by a mad scientist. "Well," she said, clearly just talking to herself now, "if they’re not integers, they might be square roots…"

"Daddy…?"

He turned around. Emily was looking up at him with wide eyes. "Yes, sweetheart?"

"What’s Mommy doing?"

He glanced back. Sarah had a graphing program running; he suspected she was now glad they’d sprung for the high-end video card that Carl had begged for so he could play his games.

"I think," Don said, turning back to his daughter, "that she’s making history."

To be young again! So many had wished for it over the years, but Donald Halifax had achieved it — and it felt wonderful. He knew his strength and stamina had ebbed these past several decades, but because it’d happened gradually he hadn’t been conscious of how much he’d lost. But it had all come rushing back over the last six months, and the contrast was staggering; it was like being on a caffeine jag all the time. The term that came to mind was "vim and vigor" — and, although he’d played "vim" often enough in Scrabble, he realized he didn’t actually know precisely what it meant, so he asked his datacom. "Ebullient vitality and energy," it told him.

And that was it! That was precisely it! His energy seemed almost boundless, and he was elated to have it back. "Zest," another word only ever employed on the Scrabble board, came to mind, too. The datacom’s synonyms for it — keen relish, hearty enjoyment, gusto — were all applicable, but the cliche "feeling like a million bucks" seemed woefully inadequate; he felt like every one of the billions of dollars that had been spent on him; he felt totally, joyously, happily alive. He didn’t shuffle anymore; he strode. Just walking along felt like the way he used to feel on those motorized walkways at airports — like he was bionic, moving so fast that it’d all be a blur to onlookers. He could lift heavy boxes, jump over puddles, practically fly up staircases — it wasn’t quite leaping tall buildings in a single bound, but it felt damn near as good.

And there was icing on this delicious cake: the constant background of pain that had been with him for so long was gone ; it was as though he’d been sitting next to a roaring jet engine for years on end, always trying to shut out the sound, to ignore it, and now it had been turned off; the silence was intoxicating. Youth, the old song said, was wasted on the young. So true — because they didn’t know what it would feel like once it was gone. But now he had it again!

Dr. Petra Jones confirmed that his rollback was complete. His cell-division rate, she said, had slowed to normal and his telomeres had gone back to shortening with each division, a new set of growth rings was starting to appear in his bones, and so on.

And the follow-up work had been completed, too. He had new lenses, a new kidney, and a new prostate, all grown from his own cells; his nose was restored to the merely honkeresque proportions it’d had in his youth; his ears had been reduced; his teeth had been whitened and his two remaining amalgam fillings replaced; and a few nips and tucks had tidied up other things. For all intents and purposes, he was physically twenty-five once more, and aging forward normally from that point.

Don was still getting used to all the wonderful improvements. His hearing was top-notch again, as was his vision. But he’d had to buy a whole new wardrobe. After the recalcification treatments and gene therapies, he’d regained the two inches he’d lost over the years, and his limbs, which had been reduced to not much more than skin and bones, had beefed up nicely. Ah, well; his collection of cardigans and shirts with buttons would have looked silly on a guy apparently in his twenties.

He’d had to stop wearing his wedding ring, too. A decade ago, he’d had it reduced in size, since his fingers had gotten thinner with age; now, it pinched painfully. He’d been waiting until the rollback was over to get it sized back up, and he’d get it done as soon as he found a good jeweler; he didn’t want to trust it to just anyone.