Add "Buy Now" button on a simple HTML page

I have a site with only one product (a book). The store is working fine but in the site front page, I use a simple HTML page with the detail of the book.

I'd like to put a button "Add to cart" or "Buy Now" that when clicked, will add 1 book to the shopping cart and direct to the check out page with 1 book in the cart.

I've been searching for this but most threads discuss how to move the "Add to Cart" button around on the store pages.

How do i add this button on a simple html page?

The "simplest" actions often require the most complex programming... My gut-feel tells me that what you want isn't easy...

Because of sessions control this is basically not possible.

Zen Cart is designed to become your site and the parts are integrated with each other and not meant to be used seperately or as pieces in another non-Zen Cart page.