It was the school run at 7:40, which she had not done since 1996 and which she had forgotten was a daily event and not a thing you do occasionally.

It was learning that a second-grade classroom now communicates entirely through an app.

It was the birthday party economy, which she had no idea existed at this scale, and the fact that every one of those parties was full of mothers in their thirties who did not know what to say to her.

It was swimming on Tuesdays, which Sophie wanted to keep doing because her mother had signed her up, and which Margaret drove her to for two years.

It was the paperwork of a child’s life — the forms, the permissions, the immunization records that were in a filing cabinet in an apartment that was now a crime scene.

And it was the specific problem of a child who had lost her mother to her father, which does not have a manual, and which Dr.