In 2025, we are no longer alone in the universe. Aliens have arrived on Earth and live peacefully with humans. At least, they do until the Troobian Empire decides to destroy Earth. The elite S.P.D. A-Squad mysteriously vanishes, leaving only the B-Squad Rangers, and their doglike alien commander, Anubis "Doggie" Cruger, to defend Earth. Two reformed thieves join the team as the Red and Yellow S.P.D. Rangers, but the other Rangers are slow to trust them. However, the team discovers they have the same origin: their parents worked for S.P.D. and created the technology for the Delta Morphers. All of the next generation have inherited unique powers that will help them save the world.
The Rangers receive a message from the future warning them that the Earth is conquered that day, but then a mysterious Omega Ranger appears from the future to help Rangers defeat the villainous Morgana, Devastation, and Shortie. Sam, the Omega Ranger, remains to help the Rangers. When the A-Squad return and capture Commander Cruger, the B-Squad must face them. Meanwhile Gruumm has transformed his ship into a body for Omni - his superior. As Broodwing has also invaded the Delta Base, the Power Rangers must combine their efforts to contain their enemies. A final showdown will reveal whether the B-Squad has the right stuff – and whether the Earth will remain free.