The movie begins with a young female spy, Lemon, infiltraiting the World Human Research Center on a mission to find someone known as the "Blue Key". Once she finds her target however, it is revealed to be Shinnosuke (or Shin-chan).
Later, back in Kasukabe, Shin-chan is seen enjoying another episode of his favorite show, Action Kamen but is shortly scolded by his parents for farting without warning. He then goes out for a walk when out of nowhere, a mask similar to Action Kamen's falls from the sky. He puts it on which then activates a short video of Action Kamen telling him to become an Action Spy: people from around the world who are supposedly friends of Action Kamen who work as secret agents to protect the world. The video also states that he will be partnered with Agent Lemon Sunomono (the girl from before) just before it self destructs. When he recovers, Lemon appears and gives him his spy uniform.
Later, back in Kasukabe, Shin-chan is seen enjoying another episode of his favorite show, Action Kamen but is shortly scolded by his parents for farting without warning. He then goes out for a walk when out of nowhere, a mask similar to Action Kamen's falls from the sky. He puts it on which then activates a short video of Action Kamen telling him to become an Action Spy: people from around the world who are supposedly friends of Action Kamen who work as secret agents to protect the world. The video also states that he will be partnered with Agent Lemon Sunomono (the girl from before) just before it self destructs. When he recovers, Lemon appears and gives him his spy uniform.