Meaning of "Did you steal the jewels?"?

Hello everyone. I am reading a novel, and I came across this expression. Could you please let me know its meaning?

“We met on Christmas Eve.”

“Yes, and?”

“And nothing. We went out a few times. Nothing happened. Now it’s over.”

Silence.

Rachel’s ex: Did you steal the jewels?

Mrs. Forsham: What a terrible question.

Me: I did not steal her jewels. But she offered to let me see them.

The ex: And?

Me: I took a rain check.

A man named David: He’s lost his mind.

- André Aciman, Eight White Nights, Seventh Night

This is a novel published in the United States of America in 2010. This novel is narrated by the nameless male protagonist who meets Clara at a Christmas party in Manhattan. Now the protagonist is talking to other people about Clara.

In this part, I wonder what the underlined expression means.

I guess it might be some euphemistic expression used to refer to a sexual intercourse, but I am not sure. And I wonder whether it is a fixed idiomatic expression...

Thank you very much for your help.