There is a really good book called Time Travel in Einstein's Universe by Richard J. Gott (http://www.amazon.com/books/dp/B003L1ZYKG http://www.amazon.com/books/

There is a really good book called Time Travel in Einstein's Universe by Richard J. Gott (http://www.amazon.com/books/dp/B003L1ZYKG http://www.amazon.com/books/dp/B003L1ZYKG) that explores different concepts of time travel and violations of causality without violating Einstein's principles of relativity.