Here's the official synopsis:
"When we last met Bill and Ted they were time-traveling teenagers trying to pass history class and win the battle of the bands. Once prophesized to save the universe with their rock and roll, middle age and the responsibilities of family have caught up with these two best friends who have not yet fulfilled their destiny. They've written thousands of tunes, but they have yet have to write a good one, much less the greatest song ever written. With the fabric of time and space tearing around them, a visitor from the future warns our heroes that only their song can save life as we know it. Out of luck and fresh out of inspiration, Bill and Ted set out on a time travel adventure to seek the song that will set their world right and bring harmony in the universe as we know it. Together with the aid of their daughters, a new crop of historical figures, and some sympathetic music legends, Bill and Ted find much, much more than just a song. The film is currently in pre-production."
Chris Matheson and Ed Solomon, the original creators of Bill & Ted's Excellent Adventure and Bill & Ted's Bogus Journey, have returned to pen the script, while Dean Parisot was confirmed to direct the film.