In any case, the detectives who knocked on Snow’s door or, more accurately, rang the buzzer, asked if they could come in, and Snow apparently said, ‘Why, what’s it about?’ When they explained that her sister hadn’t got on the plane, Snow said she knew that because her niece – meaning Ruby – had called.

My contact in the New South Wales police tells me that the police who visited that day didn’t go inside; they stood on the porch to ask their questions. Snow said her sister had arrived at around 1 p.m. and she left at around 3 p.m. and that tallied with what police knew from the CCTV at the hotel, which showed Agnes going back to her room that night.

There might be people who say police should have dug a bit deeper there and then, but remember their attention at that time wasn’t focused on what Agnes had been doing before she went missing but rather after she stepped into the dust storm.

I remember asking Ruby, back at the lunch we had at David Jones, what kind of contact she’d had with Snow in those first days after her mum went missing and she told me much the same story as my contact at Rose Bay: Snow wasn’t exactly rude, but she wasn’t much help either.

‘Mum had left me with a list of important numbers in Sydney – the number for her hotel, and Snow’s number, and so on – and as soon as I figured out that she wasn’t getting off the plane, and I couldn’t reach her by phone at her hotel, I called Snow,’ Ruby said.

‘She picked up, thank God. But when I introduced myself, she simply said, “Oh, hello.” Not, “Oh, my goodness, you must be my niece,” or anything like that. Just, “Oh, hello.”

‘I explained the situation: that Mum hadn’t got off the plane and hadn’t been in touch either, but she offered no help at all. I thought that was . . . well, perhaps not odd, but certainly a little rude. I’d made it plain, or thought I had, that I was quite frantic. I’d said, “I haven’t heard a thing from Mum, she wasn’t on the plane,” and Snow just said, “Oh?” Just like that: “Oh?”

‘I asked her, “Do you happen to know where she’s gone?” She said, “Maybe she’s sightseeing.” And I had to say, “But that would be so out of character. She normally keeps us up-to-date with what she’s doing.” Snow said, “Maybe she’s gone on a trip to the Great Barrier Reef? She said something about wanting to take some trips.” And I suppose if there was a moment when I was truly alarmed, that was the moment, because, as far as I could remember, my mother hadn’t expressed any desire to “take trips” while she was in Australia, certainly not trips that weren’t on her itinerary. In fact she had made a solemn promise to Rocco that she would not go to the Great Barrier Reef because, like most kids, Rocco was a big Steve Irwin fan and he was devastated when Steve was taken by the stingray. He made Mum promise that she would not take that risk. And yet I was being asked to believe that she’d decided to do precisely what she’d promised Rocco she wouldn’t do?’