Searching a post for certain words

Hi all, I’ve been trying to find a plugin that will enable a page/post search for individual pages and posts.
I have a blog with a few very big posts (several thousand words per post) and I want to be able to offer a search box at the top of each post that will search the content of that post only.
Much the same way that Ctrl+F in your browser does.

Does anything exist that will do this?

thanks
chris