Third Girl

Norma Restarick is young, rich and, by her own account, possibly a murderer. The heiress tells Ariadne Oliver, and then Poirot, that she thinks she may have killed someone. Everyone around her treats the confession as the fancy of a neurotic girl. Then her ex-nanny is found with her wrists slashed, and the fancy starts to look like something else.

Poirot takes the girl seriously in a way nobody else does. He moves through the people attached to the Restarick family: Andrew Restarick, Claudia Reece-Holland, Frances Cary, David Baker and Inspector Nelson, plus the nanny, Lavinia Seagram, whose slashed wrists have turned a girl's confession into a police matter. The two incidents, the suspected crime and the self-inflicted injury, turn out to be far more tightly connected than coincidence would allow. What Poirot uncovers is a conspiracy years in the making, with more than one hand in it.

Peter Flannery wrote the adaptation with Agatha Christie, and Dan Reed directed. Jemima Rooper is an excellent Norma, fragile and not quite reliable; James Wilby plays Andrew Restarick, and Zoë Wanamaker's Ariadne Oliver gets a proper share of the story, which is always welcome. David Yelland's George is on hand as ever.

What stays with you is the quiet cruelty at the centre: a family that would rather write its daughter off as neurotic than look at what is actually going on. The episode has its twists, and they land. But the sharpest thing in it is that moment of a young woman saying, out loud, that she might have killed someone, and watching the people who love her decide she is imagining it. The final reveal reorders everything you thought you knew about the household, and it is worth waiting for.

It is one of the darker Poirots of this period, and all the better for it. It repays a second watch.