In the pale glow of a half-dozen smartphone screens a shadowy figure stands half-buried in monstrous foliage. He has a blunt instrument in his hand and is stabbing it, skewering it, into something hidden in a pool of water. Behind him, through the warping glasshouse panes, there is the brooding presence of a forest from the Triassic…

I’m rather surprised that there are no classic Victorian whodunits set in botanic gardens at night. The Cambridge University tropical houses have an atmosphere of pure gothic mystery after dark. Shape-shifting alien forms, optical illusions, an aura of impending drama. I was there late last year, with a special out-of-hours pass, to witness the night blooming of the giant Amazonian water lily, the plant whose exceptional size—its pad can grow to ten feet in diameter—and ambro­sially scented flowers caused a sensation in mid-nineteenth century Britain.

The flowering is an extraordinary process. The basketball-sized bud opens as a white-petaled female, releasing an overpowering aroma of tropical fruit and raising its internal temperature eleven degrees Celsius above the surrounding air. In its natural habitat hordes of scarab beetles are attracted by the scent and warmth. A few hours later, the petals shut tight, trapping the beetles while they pick up pollen. The next evening, the flower opens again as a gorgeous pink male, releasing the beetles to carry on their pollinating cycle.

The problem for the hopeful human spectator is that the flowering is unpredictable, so I was on twenty-four-hour alert. When the call came that a flower had opened in the night, and another was due that evening, I sped to Cambridge, and was taken to the promising bud by Alex Summers, one of the curators. It seemed to be imperceptibly swelling, and there was the faintest smell of pineapple around its pool. But, as they say, a watched kettle never boils: the bud remained stubbornly cool and closed, and by ten o’clock we’d abandoned hope.

But there was one more rite to go through. In the absence (so far) of tropical scarab beetles in England, Alex has to stand in as pollinator. Up to his thighs in the lily pool, he began pushing cheap paintbrushes into the golden stamens of the previous night’s voluptuous flower. The scene was like a séance: the small circle of expectant viewers, the ghostly glow of LCD screens. “Channel the beetles, Alex,” a spectator urged. Well, he did, successfully. A great quantity of pollen was gathered, and transferred the next day to the flower that opened in its own good time after we’d gone home.