The repeat at seven the next morning showed the same.

The diagnosis is a concussion — a mild traumatic brain injury — with a brief loss of consciousness and a period of post-traumatic amnesia.

Post-traumatic amnesia is the thing nobody explains and it is the whole of Parts Twenty-Two through Twenty-Eight.

What it means is that after a head injury there is a window — minutes, hours, sometimes days — during which the person is awake, and moving, and sometimes talking, and is not laying down any memory at all.

They can hold a conversation and have no record of it twenty minutes later.