Can the theme of a series of books the first written in 1970 be continued upon without breaking copyright laws

Question

The new work will use a few of the characters names, the theme of the book, the world the book takes place in. The new work will expand on the location and theme of the orignal work, and will pick up where the previous author left off. The most recent book in the series was published in 1991.

Answer 1

The characters and possibly the 'world' would be protected by copyright. I don't know for how long. I agree you should seek permission from the original author/copyright holder. If this is not possible, consult a copyright attorney before proceeding.

Answer 2

You are on shaky ground. Contact the original authors and get permission if possible.