When Min and Yu Na's parents go missing, leaving behind only a note, the kids must make it through the day without anyone finding out - including a suspicious stranger who tries to follow them home.
Min and Yu Na learn of an important spy mission that their parents were meant to complete, involving a visit to a local enemy agent's house. With their friends' help, they embark on the mission themselves.
On Parent Teacher Night, Min and Yu Na enlist Mr Potts to step in as their grandfather. Things go well until a strange voice intercepts their radios and they realise there's an enemy agent present.
To reveal the bad spy, the kids invite the three suspects from Parent Teacher Night over for a day of interrogation, using some truth serum stolen from their parents' spy room. The answers surprise them.
The kids organise an excursion to the Botanic Gardens to intercept Mr Turei's mission - but their plan is derailed when their Halmeoni shows up unexpectedly, distracting them from their goal.
With a new mission from Halmeoni to 'protect the Seedling', Min and Yu Na divide and conquer - Yu Na managing the family hardware store while Min and his friends look after a very energetic Mr Potts.
Yu Na's birthday is ruined by everyone forgetting it, while Min's science project accidentally attracts Turmoil attention to the school. Yu Na saves the day but lands herself in detention in the process.
When Ludwig goes missing, Min risks losing his role in the school play to go looking for him - and he and Yu Na make a surprising discovery about Ms Waters during their hunt for the dog.
Min, Raph and Allegra look for a missing Mr Potts while Yu Na and Dutch get ready for the formal of a lifetime. But Mr Potts isn't where he says he is, and when they find out why, they're shocked.
Now that Turmoil has all the information it needs to destroy Tenacity (and the world) for good, the Park family must come together and use all their new skills to overthrow Turmoil once and for all.