Tananarive at dusk in August is a city of stairs. The old town climbs a ridge to the Queen’s Palace, and below it the lower town spreads along one wide avenue, in 1954 the Avenue de la Libération. The Air France office stood on it, and late on a Monday afternoon the staff had drifted outside into the last of the light.

One of them looked up. What he saw, in the account the technical chief Edmond Campagnac wrote down ten years later, was a ball of electric green light dropping towards the palace hill like the meteorite the group took it for. It went behind the ridge. Half a minute later it was back over the Government Palace, smaller and slower, and hanging over the market.

Campagnac, a former artillery officer, Polytechnique graduate and pilot, described it as a pilot would. The green ball was a lens of light. Some forty metres behind it, by his estimate, came a second shape, a cigar with the sheen of aluminium and about the length of a DC-4 fuselage, forty metres, with orange flashes at its tail. Together they swung left, sank to about a hundred metres, and ran the length of the avenue at four hundred kilometres an hour, by his reckoning. “L’engin se déplaçait sans un bruit,” he wrote: not even the hiss of a glider. Then it climbed away north-west behind the hills.

Two things followed, in his telling. The city’s lights went out beneath it and came back on behind it. And the animals went mad: dogs howled across the town, and the zebu in the livestock park stampeded. Minutes afterwards, by later reports, something identical passed low over the farm school at La Sakay, a hundred kilometres west, and scattered the herds so badly that help was sent for next morning to round them up.

General Fleurquin, commanding the French air forces on the island, is said to have ordered an inquiry and handed it to Father Coze, the Jesuit who ran the Tananarive observatory and who, by some tellings, saw the green ball fall himself. Coze supposedly took thousands of statements and concluded that twenty thousand people saw the thing. His report has never been found. A policeman’s detailed report from that night is said to have burned in a town hall fire, and the air force archives hold no trace of the inquiry at all.

The difficulty is that the most spectacular case of the French wave of 1954 rests almost entirely on one articulate witness who first published it in 1964. Investigators who went looking for the crowd found a policeman, a town hall clerk and a photographer who remembered a light but not the grand tour of the city; a former adjutant named Grimout who in 1973 recalled a far larger craft with lit portholes and ten minutes of darkness; and, in Réunion in 2004, six elderly residents who laughed or denied it. Sceptics argue for a fireball: one whose grandfather watched it that evening says it flew straight, with no double turn; another suggests the streetlamps simply obeyed their photoelectric switches when the sky lit up.

The only contemporary print is a Malagasy newspaper, Fandrosoam-Baovao, which in January 1955 ran a short piece on flying saucers over the island. It listed three. A sighting at Fort-Dauphin in September came first. Tananarive came second, placed vaguely towards the end of the year, with no date, no avenue and no Air France. The most watched object in the island’s history rated one clause, and the paper could not remember which month.