In these episodes, Thrax, the offspring of the Rangers' first enemies, Rita Repulsa and Lord Zedd, forms a coalition between the villains seeking the Corona Aurora, called The Evil Alliance. It seems Thrax's plan works since the Overdrive Rangers are defeated and cut off from the Morphing Grid. The only way to stand up to this new threat is for Sentinel Knight to assemble a team of replacement rangers made up of rangers from the past seasons. This episode brings back the Adam Park (the second Black Mighty Morphin Ranger), Bridge Carson (Red S.P.S. Ranger), Tory Hanson (Blue Wind Ranger), Kira Ford (Yellow Dino Ranger) and Xander Bly (Green Mystic Force Ranger). While most seasons of this series are isolated and don't affect the previous or following seasons directly, every now and then, the creators throw in an episode like this (like the one that featured all of the Red Rangers), I guess to make long-time fans happy. While I haven't watched the show since its third or fourth season, I was still able to appreciate this intra-series cross-over episode.
In the next episode, "One Fine Day," the rangers take a break from the hunt for the Aurora jewels, but their picnic is cut short when they run into The Fearcats, who are looking for the Centurion Torch. This is very much a standard Power Rangers episode that starts off with them fighting on foot, and them jumping into their giant robots to face off against the enemy's big bad guy. While a nice filler episode, it doesn't do a whole lot for the overall plot of the season.
"One Fine Day" is followed by another two-parter, "Ronny on Empty." When Ronny tries to throw a Halloween party, she and Will butt heads, but when she is captured by The Fearcats to power their newest creation, Will must save her. Will eventually has to team up with their enemy, Norg, in order to find The Fearcats' secret hideout, but if Ronny's life energy is drained too much by powering the creature, it could spell doom for the entire team.
Volume 4 wraps up with "Things Not Said" where some of the mysteries of the season get revealed since a computer virus reveals that The Red Overdrive Ranger, Mack, is actually an android, and he never even knew it. Ultimately, Mack has to work through the feelings of betrayal he feels towards his father and use his newly realized android abilities to stop Kamdor and Miratrix from taking the Star of Isus and transforming into the Red Sentinel Ranger.
Like the other discs in this season, the DVD is for the fans, those kids who watch the show regularly. The only appeal it might have outside of that audience would be former viewers who might find the "Once a Ranger" episodes entertaining.