kellan media

Blake Snyder called his book "The last book  on screenwriting you'll ever need"

I don't know about that. Its always good to check out other books but this is a great resource for aspiring screenwriters. 
http://www.blakesnyder.com/ (the last website on screenwriting you'll ever need)
Save The Cat and sequel Save The Cat Goes To The Movies give you an exact guide for your script structure as well as key pointers:

1. How to write an unforgettable logline
   
2. Why genre is so important to your script
3. Coming up with your hero and antagonist
4. Structure is the most important element in the writing and selling of a screenplay
5. Common sense rules of screenwriting based on experience in the trenches of Hollywood
6. Marketing your screenplay
7. The Blake Snyder Beat Sheet

Join us Snyderphiles.  If you don't want to buy the book, shame on you, buy it anyway. In the mean time, I have included the most important part: The Beat Sheet in the link above.
Don't give up on your screenplay and don't let your cat die, OK?