WILLIAM BOYD'S SECOND NOVEL, like his first, has as its central character a discombobulated young Englishman who seems bound and determined to make a hellish mess of his life. In A Good Man in Africa, published in this country a year ago, the fellow was named Morgan Leafy and his chief difficulties were alcohol and women. In An Ice-Cream War he is Felix Cobb; he is a student at Oxford during World War I, and he has his full share of vexations:

"With a sigh Felix pushed away his untasted poached eggs. Nothing in his life was going as planned; all his hopes of the past summer had proved vain and ephemeral. University was boring and lifeless, (his brother) Gabriel was at death's door in an enemy hospital, the girl he loved didn't care for him, he was heavily in debt, he had no interest in his studies, he had failed his exams, his family regarded him as a subversive malingerer and his face was disfigured by a loathsome suppurating ulcer."

Like Morgan Leafy, Felix Cobb is afforded an opportunity to lift himself out of his rut, and the opportunity presents itself in Africa. But beyond that, comparisons between the two books are of less interest or importance. A Good Man in Africa is a comic novel, its only false note being a rather sudden and unconvincing shift to a darker tone in its concluding chapters. An Ice- Cream War, though it is written with much wit and is occasionally quite hilarious, is dark throughout; its tone is appropriate to its subject, which is a world that quite unexpectedly finds itself at a point of no return.

That point is the coming of World War I, the moment in history that inspired Lord Grey's memorable words, "The lamps are going out all over Europe; we shall not see them lit again in our lifetime." But the end of the old order in Britain and the Continent has been amply treated by novelists, poets and historians, to the point where there is perhaps little or nothing left to say about it. In choosing to set his tale in Africa, therefore, William Boyd not merely frees himself to examine a familiar subject from a new angle; he also gives himself the chance to describe an aspect of the conflict that few readers are likely to be aware of--the struggle between British and German troops for control of East Africa.

The novel opens in the late spring of 1914 in the port of Dar-es-Salaam, then part of German East Africa. An American named Walter Smith has gone there from his farm just across the border in British East Africa in order to purchase supplies; he makes the return trip with a neighbor, a German named Erich Von Bishop, and his wife Liesl. Arriving at his ranch, Smith is quizzed by one of his young children about the widespread rumors of war. Laughing, he replies: "Don't be silly, Glenway. There isn't going to be a war. Well, at least not here in Africa anyways."

Yet within two months not merely is there war, but with horrifying swiftness it has come right to his doorstep. His pal Von Bishop is suddenly his enemy: "It didn't feel in the least bit like a war, yet there were enemy soldiers with loaded weapons forcibly ejecting him from his property. Von Bishop was behaving like a man who'd come round to reclaim a book he'd once lent." Just like that, and without an ounce of provocation, Smith finds himself "the only person in the whole of British East Africa who had had his land overrun and occupied." He takes his wife and children to her family's place near Nairobi, then tries without success to collect insurance compensation or state reparation for his confiscated property. A British officer tells him, "If you ask me, the only way you're going to get back to that farm of yours is to join the army and fight your way there."

Which is what he does. It is a decision that puts him on a course destined to intersect, in four years, with the progress of Felix Cobb, who has wheedled his way into the army--initially he was rejected for poor eyesight-- in hopes of tracking down his brother. Gabriel had landed with British forces in November, 1914, as part of a monumentally incompetent invasion force; he had been seriously wounded, captured and hospitalized. Now Felix, possessed by guilt and grief over his deep involvement back in England with Gabriel's young wife, is determined to find him; it is a task "born out of a mixture of near-intolerable guilt, unfocussed motives of purgation and a simple but powerful need to be doing something."

But it is a central theme of this novel that, as Walter Smith eventually points out to Felix, "Life doesn't run on railway tracks. It doesn't always go the way you expect." His noble "quest" for his brother soon enough "had fizzled out in the mud of Kibongo, his high ideals and passionate aspirations replaced by grumbles about the damp and endless speculation about what to eat." His private crusade becomes, as war almost always does for those who fight it, a mere battle for survival. And when at last the opportunity to fulfill his mission arises, the form that it takes is cruel, disenchanting and saddening; there will be no heroism for Felix.

Nor will there be, for Felix or anyone else, a return to the old and familiar life; "the world we knew before the war" was buried with its dead. In Africa as in England and Europe, the sense of certainty and confidence that had characterized the Edwardian Age was replaced, because of what happened during the war, with an "awful feeling that nothing . . . would be as sure or certain again." In the end, all Felix knows is that "you never know"--which may be, at the dawn of the modern world, something akin to wisdom.

As is appropriate to its large subject, An Ice-Cream War is populous and far-ranging. It is not dominated by any single protagonist--not even by Felix Cobb--but by a number of individuals each of whom for a time comes front and center; the war, which is always there, is its real protagonist. It takes the great themes raised by the war and translates them into the terms of ordinary lives, thereby rendering them more immediate and understandable. Further--and this was also true of A Good Man in Africa--it shows us that these individuals are endlessly surprising, never predictable; among Boyd's many strengths, certainly none is more arresting than his ability to shape his characters into complex, multi- faceted people who prove never to be exactly what we thought they were.

These people are participants in what Boyd calls "the utter randomness and total contingency of events." Few contemporary novelists have grasped this essential, inescapable truth more firmly than Boyd, and even fewer have described it with so much wit and understanding. An Ice-Cream War demonstrates beyond argument that, at 30 years of age, Boyd is already a writer of genuine stature.