THE premise of ``From Time to Time,'' Jack Finney's sequel to his immensely popular ``Time and Again,'' is that time is like a river. It carries us forward through its bends into the future. The past remains in the bends behind, however, and if the conditions are right, we should be able to reach it. At the very least, we should try.
Simon Morley, the protagonist of both books, pulls it off. He is able to travel back in time - to 1880s New York City, to be exact. The how and why of his journey in ``Time and Again,'' published in 1970, are fascinating and delightful. It's easy to see why, in the end, Morley decides to remain in a century not his own. ``Time and Again'' has just the right blend of suspense, historical detail, and good old-fashioned storytelling.
Unfortunately, ``From Time to Time'' doesn't quite measure up. Part of the problem may be the fact that sequels rarely do. Although the book can stand on its own, it's helpful to have read the predecessor. Finney seems less interested in furthering the plot or developing his characters than in simply reveling in the New York of days past.
He has a keen sense of observation, and his descriptions of a grand city carry the story along. But readers who don't share his great passion for New York might wish for more of the page-turning drama of ``Time and Again.''
Morley originally becomes involved in time travel through a government-funded project called ``The Project.'' Its founder, Dr. E.E. Danziger, had a theory. To reach the past, you must study the details of that time. Read its newspapers and books. Dress and live in its style. Think its thoughts. Then, find a place that exists in both times unchanged. Live in that place. Let the knowledge of the time you want to get to flood your mind. ``And there - in a Gateway existing in both times - you may, you just may make the transition.''
For Morley, it works. Once there, he meets a woman, Julia, marries her, and has a son Willy. After a few years, he decides to return briefly to the present, to the Project, just to see what's happening.
And that's where ``From Time to Time'' begins.
The Project has lost its funding, Morley discovers, and all that's left is the dream of one man, Ruben Prien. Prien persuades Morley to go back once more, to 1912. His mission: to stop World War I from starting.
All Morley has to do is find a man code-named ``Z,'' an aide to Presidents Taft and Roosevelt, and tamper slightly with events. Through his research, Prien discovers that ``Z'' received informal agreements from diplomats in Europe that could have averted the war. But he drowned on his way home when the ship he was sailing on, the Titanic, hit an iceberg and sank.
If Morley can ensure that ``Z'' gets home safely, agreements in hand, he can change the course of history. That means, of course, keeping the Titanic from sinking.
All this, however, is secondary to the author's real love: New York when it looked like Paris, Broadway when it was truly Broadway, ragtime and vaudeville. Morley experiences the wonder and excitement of all these things, and the author even includes photographs of New York City, circa 1912.
The reader is transported back in time with Morley when he goes to tea at the Plaza Hotel; to a lecture on dancing at Delmonico's; to the theater to see ``The Greyhound''; and up in an aeroplane for a sightseeing tour.
Only at the end, it seems, do Morley and the author remember his actual mission. Compared with the more meandering middle, the ending is rushed. But Finney clearly has a wonderful time along the way, and despite some of the book's problems, it's hard not to take pleasure in the ride.