This is book 7 of the "Maisie Dobbs" series.

This note contains spoilers for the book.

Reading out of order, which is sometimes strange in any series.

In this one, Maurice dies after being ill for a while, and Maisie agrees to court with James Compton.

The main plot goes back to WWI. Michael Clifton, an American in a British cartographic unit that was wiped out in the war comes to light, and his parents come to England to find what happened to him. They get attacked, another man gets murdered, and Maisie gets to sort it all out. Turns out Micahel was murdered before the unit was wiped out; in fact the murderer probably called in the artillery strike that wiped out the unit. (If it had been more premeditated, the original murder could have been skipped, and then the evidence that showed something was going on wouldn't have existed, and the book would have been a lot shorter and less satisfactory.)

And her friend in Scotland Yard has moved to Special Branch, so she's breaking in a new Inspector, too, one they've had trouble with before.

They find actual film footage of the man who killed Michael Clifton, being menacing even.