You're not thinking the right way - you don't pass values from some HTML to another. Clicking a link makes an HTTP request to that URL, so put the relevant data in the URL and read it in the handler. By relevant data, I mean whatever will allow you to look up the individual book. Some of this should be obvious though: the HTML is rendered on the client (i.e. the browser) and clearly the data doesn't live there, so you need to go back to the server to fetch it.
Also, why does your handler for /book need to support POST requests?
Also, why does your handler for /book need to support POST requests?