Transformers: Robots in Disguise Episode Guide
Episode 8: Secret Weapon: D-5
Original U.S. air date: September 17, 2001
Written by: Marc Handler
The Predacons steal a disk from Dr. Onishi's friend, Dr. Yoshimoto, which was supposed to be given to his son Koji. They speculate that this disk contains information on some powerful energy source or secret weapon, but are only able to salvage fuzzy images of a train numbered "D-5". Unknown to them, this train is just to be a famous coal-burning steam engine which was recently restored, in part by Dr. Onishi.
Following the D-5 out of admiration are the Autobot bullet trains, and Koji is aboard for its first trip. The Predacons repeatedly try to take the train, but are thwarted either by the Autobots or the train's own lack of computers to disrupt. Finally they steal the train at the end of its journey, intending to drive it off a cliff into the ocean where Megatron can retrieve it. Midnight Express is able to rescue it, however, and the Predacons eventually learn that the train was never a secret weapon at all.
This story was basically an excuse to spotlight Team Bullet Train again, although it also featured the rarely-heard-from Dr. Onishi. It turns out the Predacons have been keeping him unconscious until they can retrieve his knowledge of Earth's energy sources directly from his brain. Obviously, it's an inexact science. It's the last time we hear anything about Megatron's "master plan" for a while.
Besides that, we get to see a lot of blundering by Sky-Byte and the other Predacons, along with Megatron's rarely-seen "giant flying hand" mode. Midnight Express gets an extra bit of character development. The rest of it is just fun and filler.