A sequel to the classic Time and Again (1970) that, like many reprises of a once-good idea, fails to live up to the original. The novel continues the adventures of 30ish Si Morley, who while working for the Project, a secret US government research program investigating the possibility of time travel, abandoned his mission to live in the 1880s with the woman who is now his wife, Julia. Although quite at home in 19th-century New York City, Si decides to visit the present once more. Appropriately prepared- -plenty of gold coins for changing into dollars--he sits on a bench on the Brooklyn Bridge and, by visualizing the time he wants to move into, finds himself back in today's Manhattan. Within a few hours Ruben Prien, a historian and old Project hand who believes that events in the past can be changed to affect the present, has located Si and arranged a meeting. Funding has dried up for the Project (which still exists despite Si's attempts to destroy it), but interest in parallel time continues, says Ruben; in fact, he has an assignment all lined up for Si: to prevent the outbreak of World War I, without which the 20th century could be "the best, the happiest, the human race ever knew." Si travels to 1912 in search of the mysterious Z, a man commissioned by Theodore Roosevelt and William Howard Taft (though political rivals, both wanted peace) to sail to England with messages that will prevent the conflict. Si's leisurely hunt for Z often seems more a tour of vaudeville shows and New York landmarks--though a voyage on the Titanic is also necessary--than an urgent quest to save the world. The past turns out to be more obdurate than expected, and Si is left making plans for the great blizzard of 1888. Numerous old photographs and historical factoids pad the book. Zestless.