Well, I've worked out what went wrong. I was supposed, having been asked by mrph to house-sit while the new carpet was installed, to have been arriving there about eight, courtesy of Jus.
Last night I was drugged and tired, so I fell asleep before Jus got home. I had been going to remind him that I needed to be at James' place, but, being asleep, I couldn't. So he didn't wake me this morning, and therefore I wasn't at James'.
Diligent phoning finally roused me, and I made it to James' place exactly as the carpetfitter arrived. So all is good, except for having necessitated James not going into work this morning, for which I am frightfully sorry.
I am now home and in need of tea, drugs, and a lie-down.