Tsukasa's army is coming. Kinro struggles to hold the bridge against the deadly spearman Hyoga and his shock troops, but Senku and the villagers are ready with deadly new weapons of science.

Work begins on creating the components for Senku's cell phone, but spinning gold wire is proving to be quite the task! Luckily, Chrome and Kaseki "invent" the water wheel and drastically improve the process!