Monkeys, Yamamoto, and Yamada came to the sea to enjoy a summer aventure. The monkeys are reversed by two cute gal trio and enjoy the first popular period of their lives. The monkeys make friends with one of the gals, Miki, Kaori, and Kyoko, who stay in the same guest house, and make a promise to fireworks together at night. Ritsuko follows the monkeys and comes to the sea, but the monkeys flirt with Miki and bother Ritsuko. Ritsuko who got angry will go home soon. On the way back, Ritsuko went out for a drink with Takase and Uehara who had been picking up, and Mita, a rich man who joined later, liked Ritsuko. Around that time, the monkeys had a nice atmosphere with Miki enjoying the fireworks together.
ひと夏のアバンチュールを楽しもうと海にやってきたサル、山本、山田。サルらは２組のかわいいギャル３人組に逆ナンされ、人生初のモテ期を味わう。サルらは同じ民宿に泊まる片方のギャルたち、ミキ、カオリ、キョウコと仲良くなり、夜一緒に花火をする約束を交わす。リツコはサルらを追って海にやってくるが、サルはミキとイチャイチャしてリツコを迷惑がる。怒ったリツコはすぐに帰る事に。帰り道、リツコはナンパしてきた高瀬、上原と一緒に飲みに行き、後から合流したお金持ちの三田はリツコを気に入る。その頃、サルは一緒に花火を楽しむミキとイイ雰囲気になり…。
