Houtaro and his team receive information that the 102nd Chemy has unexpectedly appeared. Houtaro, Supana, and Sabimaru begin a search based on this information, and arrive at a certain research institute where Sabi's brother, Ken'ichi, works.

A new Malgam appears at the institute. Is the 102nd Chemy real after all? And behind it all is the resurrected Geryon!? Houtarou and Supana transform into Riders...!

Mami, the director of Kongo Laboratory, begs Houtaro and the others to protect the laboratory from Geryon. Protect it from Geryon? What is the relationship between Mami and Geryon...?

Houtaro, suspicious of the Chemy's behavior, asks Sabimaru if it was really Kenichi who created the Chemy. For a moment, Sabimaru is perplexed, but then he reveals the truth behind the Tsuruhara brothers and Chemies. What is that unexpected truth!?