Legal Question in Intellectual Property in Texas

You need to consult a copyright attorney before doing this as it is legally risky if not done correctly. Derivations of copyrighted works are normally infringing, but a good copyright lawyer should be able to advise you how to do this and keep it legal. This is highly specific to the facts, so it will depend on the particular show, the particular characters, how different your plot is, who you are, who you are associated with and the purpose of your movie. Call me 618-462-3450 for either a free consultation (1/2 hr) or the name of another copyright lawyer. Although I am licensed in Texas, copyright law is Federal law so the attorney can be located anywhere.

From what you've described thus far, you would be using a substantial portion of the original and not using it for the purpose of parody - for which some leeway is afforded. Consequently, the best you can do is contact the IP owner (may not be the original author) and request permmission to so use the material. If not, then you may be running afoul of copyright law.