My sister kissed my husband in front of thirty people at her own anniversary party and called it a joke. Her husband had a wrapped present in his hands and an envelope she had never opened.

And here is the thing that turned that garden over for me and that I did not understand until about four o’clock the following morning.

Two years of it.

Two years of I wish I had a husband like yours, and hanging off his arm at christenings, and the chair, and the kiss in front of our parents.

None of it was about Ellis.

It was camouflage.

You do not flirt like that with the man you are actually sleeping with. You flirt like that with a safe one, loudly, in front of everybody, for years — so that when your husband eventually gets a feeling, he has somewhere to put it.

She built Ellis into the suspect.

Tobin told me this himself, in the September, and he had worked it out in about a fortnight in the March, and he said it better than I can.

He said: “I found a receipt in the car in March. And the first thing I thought — the very first — was Ellis. Not Geth. Ellis, who lives twenty miles away and who I’ve never once seen her alone with.”