Though the Reverend Timothy Fortune had spent three years in the island of Fanua he had made but one convert. Some missionaries might have been galled by this, but Mr Fortune was a humble man who lived by the dictum 'Good things come to those who wait'.

Mr Fortune was not a scholar. For many years he had worked in a bank in Hornsey and after his godmother had bequeathed him £1000 he had been ordained as a deacon and quit England for St Fabien on the Raratongan archipelagao in the Pacific. Yet after 10 years, even St Fabien had proved a little frantic and he felt the calling to take Christianity to Fanua, an island so remote that no steamers ever visited.

The Archdeacon had not been enthusiastic. "The islanders are highly immoral," he had said. "You are not like to make many converts there."

"What, are they cannibals?"

"No, but they are like children, always singing and dancing, and they have no word for chasitity."

With those words of dry understatement, Mr Fortune understood his real mission was one of gentle satirical whimsy, so he packed his harmonium, tinned meat and other comical colonial necessities and travelled by canoe to Fanua. Several hundred islanders greeted his arrival and after spending the first night at Chief Ori's hut he retired to his dwelling on the outside of the village.

On the first Sunday, he played hymns on the harmonium and then closed his eyes in prayer. When he eventually opened them again there was a naked brown boy kneeling beside him. He gave the boy some bread and water and welcomed him with a kiss. It was a miracle! His first convert, and God had sent him.

"What is your name?" Mr Fortune asked.

"Lueli."

"I shall call you Theodore."

Lueli smiled politely. Though his mother was extremely fat, he was of a slender build, one that Mr Fortune might have described as aristocratic had the boy not been both a native and a heathen, and over the course of the next year he listened assiduously as Mr Fortune recounted the scriptures to him.

In truth, it was never really explained why a teenage native boy should so quickly have become attached to a missionary more than 30 years older than him, when the rest of the islanders took so little interest in their visitor, but the Lord moves in mysterious ways, so the reader was obliged to dismiss that niggling thought and enjoy the minutiae of their day: the early morning breakfast, the hymns, and the tiffin.

For Mr Fortune, it was enough that he had one convert and he was pleased that Lueli appeared to take as little interest as he in the bevies of girls who roamed the island licentiously. Not, of course, that either he or Lueli were in any way homosexual – though that was a sub-text some of the more prurient critics would no doubt later ascribe to their relationship in view of the author's own sexuality – but because purity was a symbol of faith and their love was of a sort that transcended physicality.

Apart, that is, from their occasional mutual oiling of bodies, a common island practice in which Mr Fortune only indulged with some reluctance and then only if he had a stiffness in the shoulders.

A year had passed when Mr Fortune followed Lueli into the jungle, where, to his shock and horror, he discovered the boy had erected a shrine to his idol. "We all have our own individual god here," Lueli had explained, for he was incapable of lying, and Mr Fortune was forced to accept the idea that he might have been premature in assuming he had even one convert. Yet Mr Fortune understood that the Christian God is a God of love and forgiveness, so he did not ask Lueli to throw away his idol and resolved instead to try harder in his teachings.

Had Mr Fortune been a little brighter, he might have realised sooner that his role in the book was to expose the futility of religious zealotry among societies that functioned perfectly happily without it, so his pursuit of Lueli's conversion was always going to be a dead end. But he wasn't very bright, so instead we were treated to further charming – if rather unnecessary – digressions.

A deep rumbling awoke Mr Fortune and as the ground shook beneath him, the harmonium toppled over, trapping him underneath and sending a lighted candle to the floor. Mr Fortune might have died in the flames had Lueli not rescued him and taken him to higher ground to escape the aftershocks of the earthquake. While Mr Fortune initially interpreted his being saved as an act of God, it was clear that to Lueli it was anything but, for his idol had been burnt in the conflagration.

Mr Fortune tried to raise Lueli's spirits, but the boy sank into an irreversible decline, a decline not helped by the other islanders teasing him for having lost his god. Mr Fortune even vaguely wondered whether he shouldn't try to find Lueli a wife – even a heathen one – but the bevy of women had as little enthusiasm for the idea as everyone else.

"I have also now lost my God," Mr Fortune eventually declared, allowing the story to tip disappointingly into overt didacticism. "I will teach you maths instead." He took Lueli to the beach to expound on Euclidian theory. "What are these?" he asked poking his stick into the sand. Lueli knew he was meant to say points, but as the whole point of the deadening episode was its pointlessness, he dutifully replied "holes", to makes sure no one missed the symbolism.

For Lueli, this was the last straw and he took himself away to the bathing pond to drown himself. Yet he hadn't counted on the tenacity of Mr Fortune, who, unable to resist a last hurrah for the stupidity of colonialism and the missionary mentality – not to mention a final triumph for the purity of unconditional love – rushed to get help and save him.

His mission had ended in failure. He headed up to the volcano to find a piece of wood and began carving Lueli a new idol. It was time for him to leave the island. His story that had begun with a bang of creative promise had fizzled out in an authorial whimper.