Empty World by John Christopher

chased across the blue sky. He felt exhilarated, and took deep breaths as he walked along the gravel path through what hadonce been the carefully tended gardens at the foot of the Memorial. Weeds grew thickly in them, and were pushing through the path as well. Further off what had been lawn was long lush grass, almost knee high.
    A few flowers survived to provide splashes of brighter colour, but the prevailing hue was green. Because of this the unexpected patch of red stood out. It was snarled in a tall briar—a standard rose that had already reverted to the primitive—and his first thought was that it was a late-flowering rose blossom. On closer view he saw it was a child’s balloon. It was sagging, more than half deflated, and he was continuing on his walk, uninterested, when he saw it had something white attached to it, a small square of card. There was writing on it.
    The briar was tall and protected by other tangled growth. Neil had to force his way in, and pull the briar down to get at the balloon. The small piece of pasteboard was limp, its edges soggy from rain, but Scotch tape had been stuck across the part carrying the message. The message itself was short and very simple:
    I am at 34 Heath Avenue,
    Hampstead. Where are you?
    Passing through Piccadilly Circus, Neil thought again of his grandfather’s remark. Anyone who waited here now in the hope of seeing a friend would be likely to have a long vigil. But one did not look for friends any more—any human being was a friend. There had been no name on the card and it had crossed his mind that it might have come from Clive. That did not bother him, either. All that mattered was that it was someone alive, and seeking contact.
    He had looked up Heath Avenue in a London street guide, and had mapped out the best route before he set off. Despite that he lost his way a ­couple of times. Once the road was blocked by debris, where fire had caused a large building to collapse outwards. Backtracking, he found himself confronted by a No Entry sign. He thought, driving past it, of the innumerable rules and regulations men had had to devise to enable them to live together on an overcrowded planet. There was only one rule left: find someone.
    He wondered about the sender of the message. He doubted if it could have been Clive. It was not the sort of thing Clive would do, and the actualmessage seemed too simple and straightforward to have come from him. The writing had been neat and attractive, well-formed without being ornate. Someone about his own age, he guessed.
    The sense of anticipation was beyond anything he could remember. It was like waiting for Christmas when he was little, but no Christmas Eve had ever been like this. It occurred to him, starting up the long slope of Haverstock Hill, that he did not know what sex the stranger was: the writing could have been either. That was unimportant, too. Soon, very soon, there would be a meeting, an end to being alone.
    He made a conscious effort to cut down the mounting excitement he felt, deliberately seeking difficulties and objections. He had no idea, for instance, how long the balloon and its card had been blowing about London—for weeks or months possibly. Whoever had sent it might have grown tired of waiting for a reply and moved on. This could be a wild goose chase.
    But his mood of expectancy and optimism easily withstood that particular cavil. The message itself was real, beyond doubt. Even if the person sendingit had moved, there would be another message saying where. Having made that attempt at communication, he was scarcely likely to leave a blank trail for someone responding to it.
    It was more likely, Neil thought with increasing animation, that he might find not one survivor but several. Probably quite a number of balloons had been launched, hundreds maybe, and others discovered sooner. There might be a whole group of people in Heath Avenue when he got there.
    He found open country surrounding