This actually isn’t an issue with the theme, the theme looks perfectly fine. It’s the plugin that you are using that isn’t setup to be responsive.
You can try contacting the plugin creators – http://support.slidedeck.com/slidedeck/ to see if they have a responsive version coming soon, or if they have a tutorial of some sort to make it responsive.
Otherwise you would probably need to hire someone to make this responsive if you want to use this plugin, as it could take some time and quite a bit of code.