Sometime in the future, scientists have discovered a diamond-shaped alien device deep in space. The mysterious alien device detonates while being probed, starting a chain reaction which destroys the entire planet. Fortunately, there's a group of slap-happy space cadets who are up in orbit who aren't affected by the explosion, but witness it, so they decide to do something about it - which means finding a way to travel back in time to avert the catastrophe before it happens!