So the only piece of information that you need to store is the virtual equivalent of a page number - no need to store any details of things like, for example, equipment that the character possesses or hit points, etc? If that is the case, this should be quite trivial - all you need to do is set a cookie with a unique name, a value of the stage that the character is at, with a reasonable expiry date - I'd suggest around a couple of weeks tops. (If somebody hasn't revisited the site after two weeks probably safe to say that they've lost interest.)
Doubtless others are available. I can't vouch for any of them as I haven't used them.
Hope this helps.