get_response will return a class from the HTTPResponse hierarchy. It's usually HTTPSuccess, but if there's a redirect, it will be HTTPRedirection. A simple recursive method can solve this, that follows redirects. How to handle this correctly is in the docs under the heading "Following Redirection."
Yes, the URLs you are retrieving appear to be returning a 302 (redirect). Net::HTTP requires/allows you to handle the redirect yourself. You typically use a recursive techique like AboutRuby mentioned (although this http://www.ruby-forum.com/topic/142745 suggests you should not only look at the 'Location' field but also for META REFRESH in the response).
open-uri will handle redirects for you if you're not interested in the low-level interaction:
require 'open-uri'
File.open("#{episode_id}.torrent", 'wb') {|torrent_file| torrent_file.write open(torrent_url).read}