– but when their experiments took them to the graveyard, the outcomes were clearly less scientific.

They squatted amongst the tombs in the drizzle, the teacher and the girls, conferring in the long grass, attracting the attention of the trio of nuns who lived in the stone enclave beyond. In a break from prayer and from the tending of the island’s green vegetables in their convent plots, the sisters watched these goings-on, initially from the shelter of the cloisters, one hand to their white headdresses so they might not lose them to the wind.

According to the sisters, Mr Hailey and the Eldest Girls were ‘searching for Chuggy Pigs’ or should they say ‘Monkey Peas’, for that was what the stranger had named them, making the girls whoop with laughter. For the purposes of the lesson, they were to write down woodlice, followed by the creature’s taxonomy – Oniscidea of the order Isopods within the class Malacostraca. The nuns admitted to joining in with the hunt for these little armoured beasts, lifting rocks and splitting tufts of grass, Mr Hailey adept at creating enthusiasm for the task.

It wasn’t insects they were searching for, he explained, but crustacea, woodlice belonging to the same taxon as lobsters or crabs. An old butter tub was populated with the animals, then the girls set about marking each one of them with a dot of paint, before releasing them again among the tombstones.

They came back a week later, Mr Hailey and the Eldest Girls, their conversation flowing effortlessly, more intimate now, something that could be deduced very easily, even from a distance, by the movement of their bodies and the gestures of their hands. They repeated the exercise – searching for woodlice and placing them in the butter tub – and were then given an equation to work out. (They hadn’t managed to escape mathematics entirely.) Take the number of animals from the first search, multiply it by the number of animals found during the second search, and then divide by the number of animals in the second sample that were marked by a dot of paint. This, the stranger explained, was the Lincoln Index.

But something had gone wrong. None of the second sample of woodlice bore the white spot, and the teacher was foxed. Had the paint he’d provided – non-toxic so as not to cause harm – washed off in the island’s insistent rains? One of the nuns, Sister Sarah, suggested that woodlice on Lark might be, unexpectedly, more nomadic than mainland woodlice and didn’t like to stay in one place for as long as a week. No one was convinced and the discussions continued. Britta Sayers, usually the most determined contributor in these kinds of situations, remained silent to the last. Only when all other possibilities were exhausted, did she offer up her conclusion, as if it had been the conclusion all along, no further argument required.

‘The marks protect them,’ she said.