Lest Eleanor think less of his father for this—the whole question of exactly whose honour was at stake was somewhat blurred in Prabir’s mind by now—he sent her a picture of Rajendra in an IRA parade, dragging a truck through the centre of Calcutta with a rope attached to his body by two metal hooks through the skin of his back. Not quite single-handed; a friend marched beside him, sharing the load. The visible tension in the ropes and the pyramids of skin raised by the hooks made it look as if both men were on the verge of being flayed alive, but they were smiling. (Smiling over gritted teeth, but anyone pushing a truck through the heat of Calcutta would have clenched their jaws as much from sheer exertion.)

A similar feat was performed as part of certain religious festivals, in which devotees would whip themselves into a frenzy of body piercing, hot-coal walking, and other supposedly miraculous acts of potential self-harm—protected by purification rituals, the blessing of a holy man, and the intensity of their faith. But Rajendra and his fellow human bullock had received no blessing from anyone, and loudly professed their complete lack of faith in everything but the toughness and elasticity of ordinary human skin. Positioned correctly, the hooks drew little blood, and a thick fold of skin could take the load easily, even if the tugging sensation was disturbing to the uninitiated. There was no need for ‘trance states’ or ‘self-hypnosis’—let alone supernatural intervention—to block out the pain or stop the bleeding, and the greatest risk of actual harm could be eliminated by carefully sterilising the hooks. It still required considerable courage to participate in such a gruesome-looking act, but knowing the relevant anatomical facts was as good an antidote to fear as any amount of religious hysteria.

Prabir spared Eleanor the picture of his mother with cheeks and tongue skewered, though like the hooks it was safe and painless enough if you knew how to avoid the larger nerves and blood vessels. The sight of his mother performing this exacting feat made Prabir intensely proud, but it also induced more complicated feelings. You couldn’t tell from the picture, and she hadn’t known it at the time, but on the day of the parade she was already carrying him. It added a certain something to his cosy images of amniotic bliss to see steel spikes embedded in the same sheltering flesh.

Rajendra had learnt of the butterfly as he was completing his doctorate in entomology. A Swedish collector, in the country on a buying expedition, had come to the university seeking help in identifying a mounted specimen he’d bought in the markets; he’d been handed down the academic ranks until he’d reached Rajendra. The butterfly—a female, twenty centimetres across, with black and iridescent-green wings—clearly belonged to some species of swallowtail: the two hind wings were tipped with long, narrow ‘tails’ or ‘streamers’. But there were puzzling quirks in certain anatomical features, less obvious to the casual observer but of great taxonomic significance: the pattern of veins in the wings, and the position of the genital openings for insemination and oviposition. After a morning spent searching the handbooks, Rajendra had been unable to make a positive identification. He told the collector that the specimen was probably a mildly deformed individual, rather than a member of an unknown species. He could think of no better explanation, and he had no time to pursue the matter further.

A few weeks later—having successfully defended his doctoral thesis—Rajendra sought out the dealer who’d sold the specimen to the Swedish collector. After chatting for a while, the dealer produced another, identical butterfly. No fewer than six had arrived the month before, from a regular supplier in Indonesia. ‘Where, exactly, in Indonesia?’ Ambon, provincial capital of the Moluccas. Rajendra negotiated the price down to something affordable and took the second butterfly to the lab.

Dissection revealed more anomalies. Whole organs were displaced from their usual positions, and features conserved across the entire order Lepidoptera were missing, or subtly altered. If all of these changes were due to a barrage of random mutations, it was hard to imagine how the creature could have survived the larval stage, let alone ended up as such a beautifully formed, perfectly functioning adult. You could expose generations of insects to teratogens until half of them grew heads at both ends of their bodies, but nothing short of a few million years of separate evolution could have produced so many perfectly harmless—or, for all Rajendra knew, beneficial—alterations. But how could this one species of swallowtail have been isolated longer than any other butterfly in the world?

Radha carried out genetic tests. Attempts to determine the butterfly’s evolutionary genealogy with standard markers yielded nonsensical results—but old, degraded DNA couldn’t be trusted. Rajendra begged the dealer to try to obtain a living specimen, but nothing doing, that was too much trouble. However, he did reluctantly reveal the name of his supplier in Ambon. Rajendra wrote to the man, three times, to no avail.

By 2006, the couple had scraped together enough money for Rajendra to travel to Ambon in person, and he’d taught himself enough Bahasa Indonesian to speak to the supplier without an interpreter. No, the supplier couldn’t get him live specimens, or even more dead ones. The butterflies had been collected by shipwrecked fishermen, killing time waiting to be rescued. No one visited the island in question intentionally—there was no reason to—and the supplier couldn’t even point it out on a map.

‘Fishermen from where?’

‘Kai Besar.’

Rajendra phoned Radha. ‘Sell all my textbooks and wire me the money.’

With the help of the bemused fishermen, Rajendra collected dozens of pupae from the island; he had no idea what the chrysalis stage would look like, so he grabbed a few examples of every variation he could find. Back in Calcutta, fifteen of the pupae completed metamorphosis, and three yielded the mysterious swallowtail.

Fresh DNA only confirmed the old puzzles, and added new ones. Structural differences in the genes for neotenin and ecdysone, two crucial developmental hormones, suggested that the butterfly’s ancestors had parted company from other insects three hundred million years ago—roughly forty million years before the emergence of Lepidoptera. This conclusion was obvious nonsense, and other genes told a far more believable story, but the discrepancy itself was remarkable.

Radha and Rajendra co-authored a paper describing their discoveries, but every journal to which they submitted it declined publication. Their observations were absurd, and they could offer no explanation for them. Most of their peers reviewing the work for the journals must have decided that they were simply incompetent.

One referee who’d read the paper for Molecular Entomologythought differently, and contacted Radha directly. She worked for Silk Rainbow, a Japanese biotechnology firm whose speciality was using insect larvae to manufacture proteins that couldn’t be mass-produced successfully in bacteria or plant cells. Her employers were intrigued by the butterfly’s genetic quirks; no immediate commercial applications were apparent, but they were prepared to fund some blue-sky research. If Radha was willing to send her DNA samples, and her own tests confirmed the unpublished results, the company would pay for an expedition to study the butterflies in the wild.

Prabir had pieced together most of this story long after the events had taken place—even when he’d been old enough to understand the fuss over the butterfly, he hadn’t been paying much attention—but he could remember the day the message arrived from Tokyo, very clearly. His mother had grabbed his hands and danced around their tiny apartment, chanting, ‘We’re going to the island of butterflies.’