Mighty Morphin Power Rangers Volume 6 is the last one before Shattered Grid. I wasn't really thinking of it as a bridge to that story line when I started reading it, as it was continuing the story of Finster's monsters who were disguised as humans. The Rangers have agreed to work with Grace, a woman who was previously a Red Ranger for a somewhat disastrous mission (her team didn't train together or know each other at all - while they ultimately saved the world, three of them died, and as the Red Ranger and leader, Grace bears that burden even though it was Zordon's fault for sending the team in unprepared). She has dedicated her life to making the world a safer place, building Promethea to accomplish that task. Her people have discovered how to track the monsters when they're getting ready to transform, and so the Power Rangers agreed to work with her.