Jerry was about to put a question, when a sudden idea struck him.

I was at my wit's end where to get the money, but a sudden idea came to me.

I said, catching at the tag end of a sudden idea.

He held out his hand and Harry, shaking it, had a sudden idea.

Do observations lead to a sudden idea or to a theory?

He lifted his head as though struck by a sudden idea.

So far he's only a sudden idea that has come into my mind.

He was about to go on when a sudden idea struck him.

A sudden idea crossed his mind but he dismissed it.

A sudden idea flashed into Nancy's mind at her friend's words.