Do you know if there is truly a "responsive" plugin that

Do you know if there is truly a "responsive" plugin that will convert a non-responsive site to a responsive site? My boss is mad at me because I told him there was no such thing, but he has another developer who has apparently used one, and now I may lose my project. I've read some really bad reviews about several WP Plugins that I Googled. I don't understand how a plugin can write styles for IDs and Classes that have names chosen by the designer, me, or how can a plugin make tables responsive (I've only found one solution to this "Responsive tables" problem, and it is using JavaScript), not to mention apps within the site that are JavaScript based or jQuery.

If I could get a WPMU DEV staff statement/answer on the issue, I think he would come around. Also, I'm certainly willing to learn if what I know at this point is wrong, but so far, I haven't been impressed with any of the reviews I've read on any of the "responsive plug-ins" that I've found. They are certainly not good enough to use on a client's site.

Your advice is greatly appreciated.