Who will pay on ‘The Undoing’ finale?

Nature or nurture?

You just know that’s a question Grace (Nicole Kidman) is asking herself after last week’s episode of HBO’s “The Undoing.”

Warning! If you didn’t watch last week’s episode, click away now! Major spoilers follow!

What makes a killer?

At the conclusion of last week’s episode, a restless Grace decided to tidy up her son Henry’s (Noah Jupe) room – and discovered the murder weapon in his violin case.

Henry awoke, looking every bit to be the guilty party who killed his father’s mistress.

Not only is Grace married to a sociopath – her lying, cheating manipulative scoundrel of a husband (Hugh Grant), she’s raising one even more monstrous.

HBO has not released a screener of the finale to reviewers. The premium cable channel wishes everyone to be surprised by the conclusion’s twists.

So, in fairness, Henry might just be hiding the weapon for his father.

It seems far more likely he killed the woman who threatened his family.

He revealed in the last episode that he knew about the affair – his father had been indiscrete at Henry’s school – and that Henry felt some responsibility for protecting his mother.

But Henry hasn’t shown any guilt about murdering another human being.

This will echo with Grace because of her conversation with Jonathan’s mother.

When he was a teenager, Jonathan had been babysitting his younger sister. She got away from him and was struck and killed by a car.

The family waited for Jonathan to experience some sort of guilt or grief. He never did. He just went on with his life.

How could Grace not have known her own son was capable of such horrific violence?

Jonathan had previously stated he suspected he knew who the killer was. It makes sense that the one sacrifice he would make in his life would be to protect his son.

It’s the sort of sacrifice Grace will respect. It’s the sort of sacrifice Grace may support.

Is she really going to turn in her tween son to the police?

Or will she stand by her husband as the state railroads him for a crime he did not commit?

Is Sylvia (Lily Rabe) hiding something? (Photo: HBO)
Is Sylvia (Lily Rabe) hiding something? (Photo: HBO)

One other thing that may come into play: At one point, Jonathan admitted there had been one other extra-marital affair, but that woman didn’t matter.

Could that woman be Nicole’s greatest confidant Sylvia (Lily Rabe)? Sylvia has seemed supportive (if sharp-tongued), and has followed the case closely.

Perhaps too closely.

There was that so-awkward wave to her pal the prosecutor when Sylvia entered the courtroom.

How would that play into Grace’s state of mind? It would be another reminder that she can trust no one in her life.

The season finale of HBO’s “The Undoing” airs Sunday at 9 p.m.