Tommy, now a captive of Mesogog, is forced to aid him in unlocking the fourth Dino Gem, or be destroyed. Meanwhile, the three Rangers stumble onto a video diary at their underground lair. Created by their mentor in case of such an emergency as this, the diary contains a recorded history of not only Dr. Oliver's life and adventures as a Power Ranger, but a summary of every team since. Even with this history lesson, the trio will need some help from a surprising source to track their mentor down!