Matt Fuller, an underachieving research assistant at one of MIT's high-tech laboratories, accidentally creates a time machine while performing routine maintenance on a graviton calibrator; the problem: the time machine only moves forward, and only in progressively exponential leaps. MIT in 2058 is not all that different from the MIT of today. The laboratory work is still tedious, the research assistants still (in their opinion) under-appreciated, and the equipment, while state-of-the-art, still jealously guarded and pitifully doled out by the supervising professors. Such is the situation Matt finds himself in. His overseer is Professor Jonathan Marsh. And while Marsh is not as bad as some, he still does not seem to fully appreciate the talents of his research assistant. Though to be fair, Matt would be hard-pressed to articulate just what these talents might be.
All of this changes for Matt during a routine calibration of a machine that measures the subtle interplay of gravitons and photons. There's a problem with the machine, though. Matt, worried that Marsh will find out and blame him, attempts to fix it. It's this idiosyncratic fix -- inexplicable and impossible to replicate -- that causes the machine to begin leaping forward in time whenever the reset button is hit.
At first, the machine disappears for only brief flashes -- mere seconds at a time. But as the periods begin to grow longer and longer, some quick calculations confirm to Matt that a roughly 12x multiplier is at play here. Matt takes the time machine and, after determining that the next jump will be short and the altered landing location due to planetary/orbital drift manageable, he decides to go along for the ride.
Matt hits the reset button and appears in a different part of Boston, precisely 39 days later. He is promptly arrested for murder, after a friend of his, who witnessed Matt's disappearance 39 days earlier, dies of shock. Unable to explain himself in any rational way, Matt is only saved once a mysterious figure bails him out and tells him to run, into the future.
Matt jumps -- 465 days into the future -- and appears in the middle of a highway, with a truck barreling down on him. He jumps again. 15 years later, he appears in a world that has been altered by the rewriting of scientific laws necessitated by Matt's time machine. To his surprise, Matt is something of a celebrity here. But his celebrity is nothing compared to that of Professor Marsh, his old boss, who has taken the lion's share of credit for the time machine and has earned himself a Nobel Prize for it. Matt feels frustrated and alienated in this new time, and decides, with little recourse, to jump again.
This time he finds himself in a repressive, neo-Medieval theocracy in the mid-23rd century. Due to spatial drift, he finds himself several hundred miles away from where he jumped. From the frightened locals, as he makes his way back to MIT, he learns that some kind of religious war has occurred. Someone calling himself "Jesus" returned and the world split between those who believed this return, and those who did not. Nuclear annihilation was the result for much of the population. Once he reaches Cambridge, Matt realizes that MIT now stands for Massachusetts Institute of Theosophy, and the school is run like a monastery, with robed apprentices and acolytes, and every lesson centered on religious truth. Matt meets a young "graduate student" named Martha, who in due time, mostly from Matt's influence, comes to realize the repugnance of her time period and agrees to accompany Matt into the future.
2000 years later, Matt and Martha find themselves on the West Coast, in a utopian society without any wants or needs. Everything is guided by a near-omipotent A.I. calling itself La. La knows they are time travelers, and obsessed with the philosophical underpinnings of her own existence, she decides to accompany them into the future. Matt begins to receive subliminal messages from an alien being calling itself "Jesus", who warns him that La intends to take them all the way to the heat death of the universe, to see if she can, in fact, die. Jesus suggests Matt and Martha keep moving forward, while stalling as much as they can, to give Jesus time to "catch up" to them. With no other option, and knowing that perhaps Jesus or some other advanced society has solved the "forward only" problem of the time machine, Matt sends them into the increasingly distant and bizarre future again and again. And again.
At last, after narrowly escaping from La, Matt and Martha meet Jesus and his followers. They contrive to send Matt and Martha back in time, while allowing La to continue on in her quest to test her mortality. The only problem is that they can only specify either the time or the location (with the time subject to a min-max range) of where they send Matt and Martha. Matt and Martha settle on location -- MIT to be exact -- since they would prefer not to end up somewhere, like the middle of the ocean, where their survival would be impossible.
Their final jump takes them back to 1898. Matt and Martha get married and decide to simply live out their lives. Matt becomes a professor and, aided by his familiarity with 20th century physics (which he is careful not to preempt), he builds a decent life for himself as a respected, if not world-shattering scientist. They live their lives. They're happy. And they die. We learn, though, in a postscript that brings the story full circle, that Professor Jonathan Marsh, the professor who inadvertently sparks Matt's entire journey, is in fact Matt and Martha's great-great-grandson.
Best part of story, including ending:
I loved Haldeman's treatment of the future societies, where humanity has altered sufficiently to make them indistinguishable from a fully alien culture. This would also be what I found so frustrating with this story: there was not enough of this societal exploration. Haldeman could have added another couple hundred pages easy.
Best scene in story:
My favorite sequence was Matt's initial arrival in the 23rd-century theocracy, as he begins to realize for the first time that the massive departures from his own timeline are, here, only the tiniest hint of what awaits him as/if he keeps jumping forward.
Opinion about the main character:
Matt was a decently plausible POV character. There was not a whole lot different or interesting about him, though, which allows him to be a relatively unbiased interpreter of the future societies, but which also leaves him seeming a little blander than he probably had to be.